[IMP] maintenance_service_http_monitoring: auto-close request on service recovery

Previously, maintenance requests created on HTTP failures were never
automatically resolved. Operators had to close them manually, with no
traceability of when or why the request was closed.

This commit adds automatic resolution when a service returns HTTP 200
while an open maintenance request exists for it.

**Detection logic** (in ``cron_check_http_services``):

Before pass 1, the cron takes a snapshot of all services that currently
have an open (non-done) ``maintenance.request`` via
``http_maintenance_request``. After pass 1, services in that snapshot
that are now OK (``http_status_ok = True``) are identified as recovered
and passed to the new ``_close_http_maintenance_request()`` method.

**Closure logic** (new ``_close_http_maintenance_request`` method):

1. Finds the first ``maintenance.stage`` with ``done = True``.
   If none exists (misconfigured instance), the method is a no-op.
2. Moves the ``maintenance.request`` to that done stage via ``sudo()``
   to bypass ACL restrictions from the cron user context.
3. Posts a chatter note on the request as OdooBot (``base.partner_root``)
   using ``subtype_xmlid="mail.mt_note"`` (internal note, not a follower
   notification) indicating the service URL and that the closure was
   performed automatically by the monitoring cron.
4. Clears ``http_maintenance_request`` on the ``service.instance``,
   allowing a fresh request to be created if the service fails again.

**Tests** (2 new, 16 total):

- ``test_service_recovery_closes_request``: full end-to-end scenario —
  first cron run produces a KO request, second cron run with HTTP 200
  asserts the request is in a done stage, the chatter note mentioning
  the service URL exists, and ``http_maintenance_request`` is cleared.
- ``test_no_close_when_no_open_request``: calling
  ``_close_http_maintenance_request`` on a service with no open request
  is a no-op and does not raise.

**README**: "Automatic Maintenance Requests" section extended with the
recovery behaviour (done stage, OdooBot note, field cleared).

maintenance_service_http_monitoring/README.md

@@ -107,6 +107,12 @@ When a service fails HTTP checks:
   after 2 seconds. A maintenance request is only created if the service fails **both**
   checks, reducing noise from transient HTTP errors
 
+When a service recovers (returns HTTP 200 after having an open request):
+- The open maintenance request is automatically moved to the first **done** stage
+- A chatter note is posted on the request by OdooBot to record the automatic closure
+- The link between the service and the request is cleared, allowing a new request to
+  be created if the service fails again in the future
+
 ## Webhook notifications
 
 When a new maintenance request is created (HTTP check failure), the module can