Motivation:
  This is the only mongoose_client_api_* module, which used
  mongoose_commands, and we are moving away from this solution
  towards a GraphQL-oriented one.
  Thus, the (soon to be deprecated) REST API needs to be simplified
  and use the *_api modules directly.

Main changes:
  - Added direct calls to mod_roster_api to mongoose_client_api_contacts
  - Added type specs for request-handling functions
  - Disabled client contacts API in mod_commands

mongoose_api_client was replaced by mongoose_client_api,
but it was still possible to configure both, confusing the user.

The only functionality lost by this change is the 'cahnge_password'
command, which was undocumented anyway.
We can readd it as 'mongoose_client_api_accounts' if needed.

Do not use mongoose_commands in the Client REST API

Added tests for domain admin in graphql_roster_SUITE. The tests are similar to those for a global admin, but they also check for permissions.

Domain admin tests in roster suite

There is two new interfaces: one simply broadcasts a new value given a
key to all workers. The other, broadcasts new important data that should
be aggregated to all available keys. This is useful if we need to modify
whatever tasks are pending.

Implement broadcasts in async pools

Extend aggregator requests and fix stall-after-error bug

This module will delegate Admin REST API calls to the handler modules,
just like mongoose_client_api is doing for client API requests.

Also: fix types in mod_roster_api

Also: fix types in mongoose_stanza_api

Marked missing error handling as TO DO - it will be done in a separate task.

Also: fix types and whitespace in mod_inbox_api

Also: fix types in mod_muc_api

Also: fix types and typos (sic!) in MUC Light modules

- Update expected messages
- Actually test message errors for MUC (invites were tested instead)
- Remove tests for listing commands and adding mongoose_commands
  Command listing will be possible only with GraphQL, and
  mongoose_commands will be removed in a follow-up PR.

Also: remove test repeat

Also: reorganize tests for easier management

Fix types in subscribeAllToAll roster GraphQL API

Unify the admin REST API

…ok format

Also: remove mod_*commands from small tests,
because this functionality is being removed.

This functionality is being removed.

This functionality is now provided by mongoose_admin_api

- Remove unused helpers from mongoose_api_common
- Move error handling to mongoose_admin_api, which is specific to the
  Admin API.
- Rework error loggiong, the log level is quite verbose (warning/error),
  but still lower than before (always error). Anyway, it applies only
  to the Admin API.

'reload_dispatch' is kept as a shell utility

Get rid of mongoose_commands

In 884ca87, with the good intention of
introducing an API to manage the accumulated affiliations, I didn't
realise the old keying was used elsewhere: in the muc cache. So we've
been missing using the cache recently. This is fixed now.

Fix cache affiliations key in the accumulator

Graphql server category

Refactored disco_local_features hook to a gen_hook format

Refactored hook handlers in ejabberd_router module

Refactored hook handlers in ejabberd_s2s module

Simplify having an extra module for a very simple function

Missing domain admin tests

Refactored hook handlers in ejabberd_sm module

This way there is only one overlay file, and the overlays work correctly
with the latest Rebar3.

As we do some templating in our tools, they need to support file
inclusion as well.

It is easier to modify vars-toml.config directly

This way we don't give the false impression of a password being checked.
It already works like this for mongoose_domain_handler.

Error messages are changed to capitalized strings, because it is the
convention used for the whole admin API.

Error codes are left as they were except ones that are already
provided by mongoose_admin_api itself, e.g. "401 Unauthorized".

The error messages should be common for REST and GraphQL,
but this unification is left for the future.

Cover the unlikely case of an invalid domain name.

Unified REST API: domains

Fix and simplify overlays

Although the functionality is not complete (e.g. some requests support
only atoms as metic names), this is not changed here.
The goal is to only replicate the existing functionality in the new
unified handlers.

It was revealed by the metric API tests.

Current logic for domain deletion first checks that the domain exists,
then removes the domain, and then runs the remove_domain hook. But this
is a problem, because if any of the hooks fails, then retrying the
domain removal won’t work, because it will be stopped at the first check
for domain existence.

Here we instead mark the domain as "in progress for deletion", which
will already disable it, and only finally delete it _after_ all hook
handlers have run hopefully successfully.

Unified REST API: metrics