feat: feature flag configurable custom backend

[dpgaspar]

SUMMARY

Add the possibility to override is_feature_enabled instead of get_feature_flags, the later when using a feature flag management system, would force all feature flags to be evaluated when evaluating a single feature.

IS_FEATURE_ENABLED_FUNC and GET_FEATURE_FLAGS_FUNC should be mutually exclusive (but not obligatory) has stated on the config comments, this is because get_feature_flags will call is_feature_enabled to make the API consistent and safe to get all feature flags and be sure that all gets applied on the override.

Introduces a new Config key:

IS_FEATURE_ENABLED_FUNC: Callable that overrides current is_feature_enabled

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

@jfrag1

[codecov]

Codecov Report

Merging #16618 (f4472aa) into master (788c0c3) will increase coverage by 0.07%.
The diff coverage is 88.65%.

❗ Current head f4472aa differs from pull request most recent head 1b9b4fe. Consider uploading reports for the commit 1b9b4fe to get more accurate results

@@            Coverage Diff             @@
##           master   #16618      +/-   ##
==========================================
+ Coverage   76.76%   76.83%   +0.07%     
==========================================
  Files        1004     1005       +1     
  Lines       53967    54014      +47     
  Branches     7335     7337       +2     
==========================================
+ Hits        41430    41504      +74     
+ Misses      12298    12270      -28     
- Partials      239      240       +1     

Flag	Coverage Δ
hive	81.24% <88.09%> (+0.08%)	⬆️
mysql	81.66% <88.09%> (+0.12%)	⬆️
postgres	81.62% <88.09%> (+0.06%)	⬆️
presto	?
python	82.05% <88.09%> (-0.06%)	⬇️
sqlite	81.33% <88.09%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...mponents/nativeFilters/FiltersConfigModal/utils.ts	72.22% <ø> (-1.39%)	⬇️
...nd/src/dashboard/components/nativeFilters/utils.ts	56.25% <ø> (ø)
superset/db_engine_specs/base.py	88.39% <ø> (ø)
superset/db_engine_specs/presto.py	84.51% <ø> (-5.44%)	⬇️
superset/reports/api.py	88.46% <ø> (+0.67%)	⬆️
superset/sql_lab.py	80.70% <ø> (ø)
superset/views/core.py	76.00% <81.48%> (+0.37%)	⬆️
superset-frontend/src/components/Select/Select.tsx	89.95% <88.88%> (+17.30%)	⬆️
...onfigModal/FiltersConfigForm/FiltersConfigForm.tsx	73.20% <100.00%> (+0.07%)	⬆️
...nd/src/dashboard/components/nativeFilters/types.ts	100.00% <100.00%> (ø)
... and 18 more

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[jfrag1]

I think this feature flag backend would also need to be able to evaluate all feature flags to send via bootstrap here. Otherwise, you'd still need to define a GET_FEATURE_FLAGS_FUNC to get the proper values to the frontend, which seems like it would defeat the purpose of having a custom backend.

Update:
Disregard, I see now that this can also be achieved with the COMMON_BOOTSTRAP_OVERRIDES_FUNC config. It may be good to make a note that it is required to do this to ensure flags are consistent between bootstrap and the custom backend

[dpgaspar]

I think this feature flag backend would also need to be able to evaluate all feature flags to send via bootstrap here. Otherwise, you'd still need to define a GET_FEATURE_FLAGS_FUNC to get the proper values to the frontend, which seems like it would defeat the purpose of having a custom backend.

Update:
Disregard, I see now that this can also be achieved with the COMMON_BOOTSTRAP_OVERRIDES_FUNC config. It may be good to make a note that it is required to do this to ensure flags are consistent between bootstrap and the custom backend

Actually that's a good point, I made a refactor on this PR to directly override is_feature_enabled it's simpler and ended up being simpler to integrate on our side. No need to make the note on the config, since get_feature_flags maps all flags to is_feature_enabled when the override is set.

[craig-rueda]

LGTM

[jfrag1]

LGTM

[villebro]

LGTM with a few miniscule nit suggestions 👍