[Utility] Create trustless_relay_validation.md (#938)

## Description

Add diagrams to describe validations done on trustless relays. Part of
work on #918

## Issue

Fixes #918 

## Type of change

Please mark the relevant option(s):

- [ ] New feature, functionality or library
- [ ] Bug fix
- [ ] Code health or cleanup
- [ ] Major breaking change
- [X] Documentation
- [ ] Other <!-- add details here if it a different type of change -->

## List of changes

- Add a new markdown file to show trustless relay validations.

## Testing

- [ ] `make develop_test`; if any code changes were made
- [ ] `make test_e2e` on [k8s
LocalNet](https://github.com/pokt-network/pocket/blob/main/build/localnet/README.md);
if any code changes were made
- [ ] `e2e-devnet-test` passes tests on
[DevNet](https://pocketnetwork.notion.site/How-to-DevNet-ff1598f27efe44c09f34e2aa0051f0dd);
if any code was changed
- [ ] [Docker Compose
LocalNet](https://github.com/pokt-network/pocket/blob/main/docs/development/README.md);
if any major functionality was changed or introduced
- [ ] [k8s
LocalNet](https://github.com/pokt-network/pocket/blob/main/build/localnet/README.md);
if any infrastructure or configuration changes were made

## Required Checklist

- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have added, or updated, [`godoc` format
comments](https://go.dev/blog/godoc) on touched members (see:
[tip.golang.org/doc/comment](https://tip.golang.org/doc/comment))
- [ ] I have tested my changes using the available tooling
- [ ] I have updated the corresponding CHANGELOG

### If Applicable Checklist

- [ ] I have updated the corresponding README(s); local and/or global
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have added, or updated,
[mermaid.js](https://mermaid-js.github.io) diagrams in the corresponding
README(s)
- [ ] I have added, or updated, documentation and
[mermaid.js](https://mermaid-js.github.io) diagrams in `shared/docs/*`
if I updated `shared/*`README(s)

utility/doc/README.md

@@ -27,6 +27,8 @@ And implement the basic transaction functionality:
 - Pause
 - Unpause
 
+And implement [the trustless relay validation and execution](TRUSTLESS_RELAY_VALIDATION.md)
+
 Added governance params:
 
 - BlocksPerSessionParamName

utility/doc/TRUSTLESS_RELAY_VALIDATION.md

@@ -0,0 +1,73 @@
+# Validation of Trustless Relays
+
+- [A. Client-side Relay Validation](#a-client-side-relay-validation)
+- [B. Server-side Relay Validation](#b-server-side-relay-validation)
+
+## A. Client-side Relay Validation
+
+When an application requests to send a trustless relay, the CLI performs several checks on the relay before sending it to the specified servicer.
+The following diagram lists all these checks with links to the corresponding code secion (or an issue if the check is not implemented yet).
+
+```mermaid
+---
+title: Client-side Relay Validation
+---
+graph TD
+    app_key{<b><a href='https://github.com/pokt-network/pocket/blob/bfc57eb89907932831b5730c68a09b4656c420c2/app/client/cli/servicer.go#L91'>Validate app key</a></b>}
+    session{<b><a href='https://github.com/pokt-network/pocket/blob/bfc57eb89907932831b5730c68a09b4656c420c2/app/client/cli/servicer.go#L163'>Validate the Session</a></b>}
+    servicer{<b><a href='https://github.com/pokt-network/pocket/blob/bfc57eb89907932831b5730c68a09b4656c420c2/app/client/cli/servicer.go#L133'>Validate the Servicer</a></b>}
+    payload{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/app/client/cli/servicer.go#L191'>Deserialize Payload</a></b>}
+    relay{<b><a href='https://github.com/pokt-network/pocket/issues/943'>Validate relay contents</a></b>}
+    send[<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/app/client/cli/servicer.go#L177'>Send Trustless Relay to the provided Servicer</a></b>]
+    user_err[Return error to user]
+
+    app_key-->|Failure| user_err
+    session-->|Failure| user_err
+    servicer-->|Failure| user_err
+    payload-->|Failure| user_err
+    relay-->|Failure| user_err
+
+    app_key-->|Success| session
+    session-->|Success| servicer
+    servicer-->|Success| payload 
+    payload-->|Success| relay
+    relay-->|Success| send
+```
+
+## B. Server-side Relay Validation
+
+Once a trustless relay has been received on the server side, i.e. by the servicer, several validations are performed on the relay. 
+The following diagram outlines all these checks along with links to the corresponding section of the code (or to an issue if the check has not been implemented yet)
+
+```mermaid
+---
+title: Server-side Relay Validation
+---
+graph TD
+    deserialize{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/rpc/handlers.go#L85'>Deserialize Relay Payload</a></b>}
+    meta{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/utility/servicer/module.go#L210'>Validate Relay Meta</a></b>}
+    chain_support{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/utility/servicer/module.go#L221'>Validate chain support</a></b>}
+    session{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/utility/servicer/module.go#L378'>Validate the Session</a></b>}
+    height{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/utility/servicer/module.go#L496'>Validate Relay Height</a></b>}
+    servicer{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/utility/servicer/module.go#L332'>Validate Servicer</a></b>}
+    mine_relay{<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/utility/servicer/module.go#L254'>Validate the app rate limit</a></b>}
+    execute[<b><a href='https://github.com/pokt-network/pocket/blob/f41039b42ce628f73afe27b7f7b6111cca085cf0/utility/servicer/module.go#L191'>Execute the Relay</a></b>]
+    client_err[Return error to client]
+
+    deserialize-->|Failure| client_err
+    meta-->|Failure| client_err
+    chain_support-->|Failure| client_err
+    session-->|Failure| client_err
+    height-->|Failure| client_err
+    servicer-->|Failure| client_err
+    mine_relay-->|Failure| client_err
+    
+    deserialize-->|Success| meta
+    meta-->|Success| chain_support
+    chain_support-->|Success| session
+    session-->|Success| height
+    height-->|Success| servicer
+    servicer-->|Success| mine_relay
+    mine_relay-->|Success| execute    
+```
+<!-- GITHUB_WIKI: utility/trustless_relay -->