Keep track of activity's channels

[pk82869]

Changes proposed ✍️

This PR contains code for the following.

• Creating a migration for adding a column called activityChannels in Settings table.
• This Column is kept up to date using the add activity API, when new channels are encountered, they are then updated in the settings table in the respective platform.

Checklist ✅

• Label appropriately with Feature, Enhancement, or Bug.
• Tests are passing.
• New backend functionality has been unit-tested.
• Environment variables have been updated:
  • Local frontend configuration: frontend/.env.dist.local, frontend/.env.dist.composed.
  • Local backend: backend/.env.dist.local, backend/.env.dist.composed.
  • Configuration docs have been updated.
  • Team members only: update environment variables in override, staging and production env. files and trigger update config script.
• API documentation has been updated (if necessary) (see docs on API documentation).
• Quality standards are met.
• All changes have been tested in a staging site.
• All changes are working locally running crowd.dev's Docker local environment.

[joanreyero]

Thanks a lot for your contribution! 🤩🙏
The changes look great, and the new functionality will be super appreciated.

I added a couple of nitpicks. Once they are addressed, I will prepare a query to change past data and we can merge!

[joanreyero]

Nit: I don't think this is needed. Can you remove it? 😊 so we don't have commented code

[joanreyero]

Nit: the getActivityChannels function is not async. No need to await.

[CLAassistant]

All committers have signed the CLA.