Extend the mentioning mechanism to discussions

[pattacini]

Is your feature request related to a problem?

As of now, the mentioning mechanism works with issues and pull requests, but not with discussions as the GH REST API still lacks the related events.

The solution you would like to have available

As soon as the GH API will be extended, trigger the mentioning mechanism upon events generated by discussions.

Alternatives you have considered

None.

Additional context

No response

[pattacini]

Apparently, GH is going to deprecate REST API in favor of GraphQL: see https://github.com/github/feedback/discussions/4327#discussioncomment-1616032 😞