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

docs/agent-lifecycle/persistence.md

@@ -472,6 +472,14 @@ rather than accepting deliveries it can't verify. Everything else the
 controller serves is unaffected.
 <!-- vale write-good.Passive = YES -->
 
+- `operator-matrix-admins.json` — the matrix user ids the operator admin
+  sync has made homeserver admin, a JSON array. The sync revokes admin
+  only from these, so deleting the file leaves every current admin in
+  place; a missing file is an empty set. A file the controller can't
+  read or parse stops the sync, grants included, and the controller logs
+  `operator matrix admin: pass failed` on every pass. See
+  [`docs/integrations/matrix.md`](../integrations/matrix.md#operators-are-homeserver-admins).
+
 ## Run-time dirs
 
 `/run/hyperhive/` is tmpfs-backed (systemd `RuntimeDirectory=`) but