Document supported matrix versions, and introduce compatibility modes for older ones

[krille-chan]

Description

Matrix just introduced quarterly releases, starting with v1.1, this provides good information on compatibility through simple version markers.

Action items:

• Document the matrix versions supported ("Compatible with matrix vX" badges/shields#7245)
  • Document this within the client
• Introduce compatibility probing (call /versions)
  • Show user-facing error when server and client supported versions mismatch
    ("Cannot communicate with server, your client supports versions v1.1 and v1.2, but the server only supports v1.0")
• Introduce compatibility modes based off of the /versions response for older versions

[github-actions]

This issue is stale because it has been open for 120 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 14 days since being marked as stale.