Add UI in settings to change ID Server
Just changes the current ID server being used
To come in subsequent PRs:
* Store this in account data
* Check for terms or support the proper UI for accepting terms when setting
* Support disconnecting
Part 1 of https://github.com/vector-im/riot-web/issues/10094
Requires https://github.com/matrix-org/matrix-js-sdk/pull/1013
