Add group override for Matrix

[Givemeurcookies]

Describe the feature request

Currently a lot of the alerting features have overrides for groups however Matrix doesn't seem to have this according to the documentation.

From my understanding you can use "provider-override" on each endpoint to get around this issue but it requires a lot of extra config when you might simply want to have the status of i.e development/test applications to be posted to a different channel than the production environment.

Why do you personally want this feature to be implemented?

We only need to the internal room id field to be different for some of the endpoint groups, however to keep the alerting functionality similar/consistent, it would make sense to implement all the other features that is standard for other integrations.

How long have you been using this project?

No response

Additional information

No response