[Persistence] Document how different data structures and engines are used

[Olshansk]

Objective

Make it clear and accessible to newcomers to the database how (and why) data is store in a certain way.

Origin Document

#847 (comment)

Starting Point

This table can be used as a starting point

Tree Type	Storage Type	Responsibility
IBC Tree	KV Store	State Commitment
IBC Tree	KV Store	State Storage
IBC Tree	KV Store	Data Integrity
IBC Tree	KV Store & Block Store	Data Availability
Other Trees	KV Store	State Commitment
Other Trees	Postgres	State Storage
Other Trees	KV Store	Data Integrity
Other Trees	KV Store & Postgres & Block Store	Data Availability

Goals

• Document how data is stored across different data structures and database engines
• Make it clear why data is stored in a certain way

Deliverable

• Clarify the following things like:
  • Where are we storing values vs hashes
  • Where/how is the KV store
• Update the following (where appropriate) documentation:
  • https://github.com/pokt-network/pocket/tree/main/persistence/docs
  • https://github.com/pokt-network/pocket-network-protocol/tree/main/persistence

Non-goals / Non-deliverables

• Changes to the architecture or implementation

General issue deliverables

• Update the appropriate CHANGELOG(s)
• Update any relevant local/global README(s)
• Update relevant source code tree explanations
• Add or update any relevant or supporting mermaid diagrams

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Creator: @Olshansk
Co-Owners: @dylanlott @h5law