Fix delete_old_otks job on worker deployments

[richvdh]

In a worker-mode deployment, the E2eKeysHandler is not necessarily loaded, which means the handler for the delete_old_otks task will not be registered. Make sure we load the handler.

Introduced in #17934

[richvdh]

Without this, it fails repeatedly with:

2024-11-25 16:08:01,943 - synapse.metrics.background_process_metrics - 253 - ERROR - launch_scheduled_tasks-97870 - Background process 'launch_scheduled_tasks' threw an exception
Capture point (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/synapse/src/synapse/app/generic_worker.py", line 367, in <module>
    main()
  File "/home/synapse/src/synapse/app/generic_worker.py", line 363, in main
    start(sys.argv[1:])
  File "/home/synapse/src/synapse/app/generic_worker.py", line 358, in start
    _base.start_worker_reactor("synapse-generic-worker", config)
  File "/home/synapse/src/synapse/app/_base.py", line 139, in start_worker_reactor
    start_reactor(
  File "/home/synapse/src/synapse/app/_base.py", line 204, in start_reactor
    run()
  File "/home/synapse/src/synapse/app/_base.py", line 186, in run
    run_command()
  File "/home/synapse/src/synapse/app/_base.py", line 124, in <lambda>
    run_command: Callable[[], None] = lambda: reactor.run(),
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/base.py", line 701, in run
    self.mainLoop()
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/base.py", line 709, in mainLoop
    self.runUntilCurrent()
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/base.py", line 1063, in runUntilCurrent
    f(*a, **kw)
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 873, in callback
    self._startRunCallbacks(result)
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 980, in _startRunCallbacks
    self._runCallbacks()
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 1074, in _runCallbacks
    current.result = callback(  # type: ignore[misc]
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 1960, in _gotResultInlineCallbacks
    _inlineCallbacks(r, gen, status, context)
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 2112, in _inlineCallbacks
    status.deferred.callback(callbackValue)
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 873, in callback
    self._startRunCallbacks(result)
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 980, in _startRunCallbacks
    self._runCallbacks()
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 1074, in _runCallbacks
    current.result = callback(  # type: ignore[misc]
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 873, in callback
    self._startRunCallbacks(result)
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 980, in _startRunCallbacks
    self._runCallbacks()
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 1074, in _runCallbacks
    current.result = callback(  # type: ignore[misc]
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 1960, in _gotResultInlineCallbacks
    _inlineCallbacks(r, gen, status, context)
  File "/home/synapse/env-python311/lib/python3.11/site-packages/twisted/internet/defer.py", line 2014, in _inlineCallbacks
    result = context.run(gen.send, result)
Traceback (most recent call last):
  File "/home/synapse/src/synapse/metrics/background_process_metrics.py", line 251, in run
    return await func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/synapse/src/synapse/util/task_scheduler.py", line 339, in _launch_scheduled_tasks
    await self._launch_task(task)
  File "/home/synapse/src/synapse/util/task_scheduler.py", line 392, in _launch_task
    raise Exception(
Exception: No function associated with action delete_old_otks of the scheduled task delete_old_otks_task