[FIX] Discussion not updating rooms list and not checking right permissions

[sampaiodiego]

Proposed changes

Validate if a user can send message on the channel he/she is trying to create the discussion.

Also update rooms list when a discussion is created.

Issue(s)

Closes #15430

How to test or reproduce

• Mute an user on a room, with that user, create a discussion to that room
• After creating a discussion check on other user's rooms list and the room will not be updated.

Screenshots

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves a current function)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Hotfix (a major bugfix that has to be merged asap)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Changelog

Further comments