fix(detectors): Require data sources for Detector creation by default

[kcons]

This ensures that Detectors require data sources to be created by default, with an opt-out for DataSource-less cases.

Fixes SENTRY-5KZC.

[malwilley]

Should we put this in the base class or are there some detectors that don't need data sources?

[github-actions]

Backend Test Failures

Failures on a8cd866 in this run:

tests/sentry/workflow_engine/detectors/test_error_detector.py::TestErrorDetectorValidator::test_create — log

tests/sentry/workflow_engine/detectors/test_error_detector.py:35: in test_create
    assert validator.is_valid()
E   assert False
E    +  where False = <bound method BaseSerializer.is_valid of ErrorDetectorValidator(context={'organization': <Organization at 0x7f809db04e...lly resolve an issue if it hasn't been seen for this many hours. Set to `0` to disable auto-resolve.", required=False)>()
E    +    where <bound method BaseSerializer.is_valid of ErrorDetectorValidator(context={'organization': <Organization at 0x7f809db04e...lly resolve an issue if it hasn't been seen for this many hours. Set to `0` to disable auto-resolve.", required=False)> = ErrorDetectorValidator(context={'organization': <Organization at 0x7f809db04e10: id=4557764654333952, owner_id=None, n...ally resolve an issue if it hasn't been seen for this many hours. Set to `0` to disable auto-resolve.", required=False).is_valid