swarm-controller: revoke matrix admin from former operators

The operator admin sync now also takes homeserver admin away. It records
each user id it sends `make-user-admin` for in
`operator-matrix-admins.json` under the controller's state directory
(written to a temporary file and renamed over it; a missing file is an
empty set). On each pass, a recorded account that is no longer in
authelia's `admins` group but is still joined to `#admins:<server>` is
sent `!admin users force-leave-room <user> <admin room id>` as `@swarm`,
over the same `/_matrix` path the grant uses. Leaving that room is what
ends tuwunel admin.

It never revokes an admin it didn't grant, `@swarm`, tuwunel's server
user (`@conduit:<server>`), an agent's account (the store's
`hive-agent-*` cert roles, the same roster the agent account mint uses),
or anyone in the new `services.hyperhive.swarm.matrix.adminSync.ignoreUsers`
list. That list reaches the daemon as
`SWARM_CONTROLLER_MATRIX_ADMIN_SYNC_IGNORE_USERS`. It also never sends a
revoke that would leave `#admins` with no member besides `@swarm` and the
server user.

A revoke is sent at most once per account per controller process, like a
grant. A recorded account that is out of both the group and the room is
dropped from the file.

Closes #4799

nix/host-modules/swarm-controller.nix

@@ -877,6 +877,10 @@ in
         # nothing about it is unsafe to define on a host whose queue is
         # off (the daemon just has nothing to apply it to).
         SWARM_CONTROLLER_STALE_AFTER_SECS = toString cfg.staleAfterSeconds;
+        # The accounts the operator admin sync never revokes. Whitespace-
+        # separated: a matrix user id cannot contain a space. Consumed by
+        # swarm-controller/src/matrix_account/operator_admin.rs.
+        SWARM_CONTROLLER_MATRIX_ADMIN_SYNC_IGNORE_USERS = lib.concatStringsSep " " matrixCfg.adminSync.ignoreUsers;
       }
       // queueEnv
       // forgeEnv