EA: Link to MAS for sign-out of other devices in MSC3824 OIDC-aware mode

[hughns]

Element Android was previously made "OIDC-aware" (as described by MSC3824).

In the case of OIDC-aware clients, you cannot sign out of other sessions via the device manager in EA anymore. Instead, users will need to be guided towards the MAS UI to take this actions.

MSC3824 now describes this requirement including a format of a deep link structure to pass the device ID: ?action=session_end&device_id=<device_id>

[pmaier1]

• We should add wording to let the user understand what's happening: "You will be redirected to your server's authentication provider to complete sign out."
• If the server doesn't advertise an account management URL, the client should show a message saying that the functionality is currently unavailable and the user should contact the administrator.

[pmaier1]

This is how iOS implements it element-hq/element-ios#7658

[pmaier1]

@bmarty from testing, we've found that there is no prompt to let the user know what's actually happening, ref. #8616 (comment). Can you check?