Feature Request: flag rooms with bridge information [MSC2346]

[BrainDamage]

MSC2346 allows to specify extra information for the bridge status of rooms that have to be otherwise guessed or provided externally otherwise.
Matrix-appservice-irc already supports this, as well as many bots from the mautrix umbrella. Element has support to display the information, currently gate under a labs flag

The spec is not finalized, so it's liable to change. Glancing at the reviews however, it seems that the amount of forseeable changes would be pretty limited limited in scope, and could be amended as necessary once finalized, letting users benefit already from current definition