feat: respect the room avatar external provider url setting

[reinaldonetof]

Proposed changes

This Room Avatar External Provider Url was implemented to the server at: RocketChat/Rocket.Chat#18929

This PR respects the room avatar external provider URL at the server: RocketChat/Rocket.Chat#28910

Issue(s)

How to test or reproduce

• Get a link to an image
• As a workspace admin, go to Administration -> Workspace
• Then go to Settings -> Accounts -> Avatar -> Room Avatar External Provider URL
• paste the link there
• save

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)
• 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

Further comments

TC-616