These are used to store settings for individual communities a
user is part of, either as member or as owner.
This included whether or not the community history archive protocol
is enabled.
This adds a new `CommunitySettings` type and adds
a migration script that introduces a new `communities_settings`
table.
It also extends the `MessengerResponse` type to include
`CommunitySettings` which are honored when communities are being
added, edited, joined or left.
Lastly, this adds a new RPC API to retreive the settings.
Closes#2564
bf8e71cfa9