Document supported features per bridge

[selfhoster1312]

Upstream features are not well documented yet:

• is the feature supported for this bridge?
• since what version is this feature supported for this bridge?
• does it work both ways? (some features such as puppeting only make sense one way, but eg. replies need bidirectional support when receiving replies, and when sending replies)
• is there specific implementation quirks to know about? (link to the docs)
• is there already a tracking issue for implementation if it's not supported yet?
• is there already proposed PRs to implement it that need testing/review?

I think we should have a proper feature matrix in a YAML/TOML file in the repository, with a script that updates a docs/features.md page accordingly. The script should warn when some feature was not declared supported/unsupported for a specific bridge.

[poVoq]

While nice in theory, I think making and maintaining such a feature matrix will be a huge time sink.

[selfhoster1312]

maintaining such a feature matrix

I think once the docs are in the same repo (#6), it will be easier to keep it up-to-date. It would be part of the contribution process in the docs that i should update docs/features.yml with the new features the PR is adding to a specific bridge.

The main problems are imho:

• filling the current state of the feature matrix
• writing tests to ensure it stays that way