Local Feature Flag Evaluation

[EDsCODE]

• GetAllFlags
• Adjust IsFeatureEnabled and GetFeatureFlag to share logic
• Local Evaluation supported
• api/feature_flag updated to local_evaluation endpoint
• New suite of tests according to (https://github.com/PostHog/posthog/issues/10459#issuecomment-1193842228)

[EDsCODE]

TODO:

• [x] default value tests
• [ ] feature_flag_called instrumentation and testing
• [ ] memory tests + sizelimiteddict
• [x] Make sure current tests have max coverage of options that match spec
• [x] onlyevaluatelocally and sendfeatureflag arguments
• [ ] warn/debug logging
• [x] inactive flag test
• [x] personalapikey loading test/wrong key test