Client failing on getting all feature flags

[DominicOram]

When hyperion calls the config server to get all the feature flags it fails with:

[31m[E 240712 10:12:17.954 client:84] Encountered an error reading from the config service.�[0m
Traceback (most recent call last):
  File "/dls_sw/i03/software/bluesky/hyperion_v9.5.1/hyperion/.venv/lib/python3.11/site-packages/daq_config_server/client.py", line 82, in best_effort_get_all_feature_flags
    return self._get(ENDPOINTS.FEATURE, options={"get_values": "true"})
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/dls_sw/i03/software/bluesky/hyperion_v9.5.1/hyperion/.venv/lib/python3.11/site-packages/daq_config_server/client.py", line 41, in _get
    assert item in body, f"Malformed response: {body} does not contain {item}"
           ^^^^^^^^^^^^
AssertionError: Malformed response: {'set_stub_offsets': False, 'use_panda_for_gridscan': True, 'use_gpu_for_gridscan': True} does not contain None

Acceptance Criteria

• Calling best_effort_get_all_feature_flags does not fail
• There are tests for this

[dperl-dls]

This should already be fixed by #49