[v0/v1 migration] Have flask is_feature_flag logic fetch request from context, add flag for v2/recognize/places

[juliawu]

This PR:

• Updates the is_feature_enabled() function in our flask server to fetch the request from context if available (and if an explicit request object is not provided).
• As proof of concept, this PR also implements a flag check for switching between v1/recognize/places and v2/recognize/places.
• Adds the use_v2_api flag to feature_flags.py to implement the above bullet point.

This will allow us to get enable_feature= query parameter values from requests without needing to pipe in the request object through very deep stacks of calls. On the client side, we would just need to ensure enable_feature= is included in the request to flask APIs. For example, even if we are on datacommons.org?enable_feature=use_v2_api, if that page makes a call to api/route, we would need to update the client side code to make a call to api/route?enable_feature=use_v2_api.

Testing:
To verify this flow, I added logging statements to dc.recognize_places() and verified that:

Uses V1 API
http://localhost:8080/explore?enable_feature=enable_stat_var_autocomplete#q=jobs%20in%20texas

Uses V2 API
http://localhost:8080/explore?enable_feature=enable_stat_var_autocomplete&enable_feature=use_v2_api#q=jobs%20in%20texas

Note that this page does not make a separate request to the flask apis, so no extra enable_feature=use_v2_api piping was needed.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request improves the developer experience for handling feature flags by reducing the need to manually pass request objects through deep call stacks. It also establishes a mechanism for A/B testing or gradual migration between API versions by implementing a configurable flag for the recognize places service.

Highlights

• Context-aware feature flags: Updated the is_feature_enabled function to automatically resolve the request object from the Flask request context if not explicitly provided.
• API Versioning: Introduced a USE_V2_API feature flag to allow toggling between v1 and v2 endpoints for place recognition.

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[gemini-code-assist]

Code Review

This pull request introduces a USE_V2_API feature flag to toggle between V1 and V2 versions of the recognize_places endpoint, updates the feature flag utility to automatically handle Flask request contexts, and adds the V1 endpoint to the service discovery list. I have no feedback to provide.

[juliawu]

Closing in favor of separate PRs, one for the v*/recognize/places, the other for the update to is_feature_enabled()

[gmechali]

LGTM, thanks

[juliawu]

Closing, these changes have been implemented in #6156 and #6159