refactor: Removes the deprecated KV Store feature

[michael-s-molina]

SUMMARY

As part of the 4.0 approved initiatives, this PR removes the deprecated KV Store feature and its related assets such as the API endpoint, the keyvalue table, and the KV_STORE and SHARE_QUERIES_VIA_KV_STORE feature flags.

The previous value of both feature flags was False and now the feature is permanently removed.

TESTING INSTRUCTIONS

CI should be sufficient for merging this PR. We'll do a complete testing of 4.0 after all approved proposals are merged.

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (863f8bb) 69.18% compared to head (1fda831) 69.13%.
Report is 18 commits behind head on master.

Additional details and impacted files

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##           master   #26376      +/-   ##
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- Coverage   69.18%   69.13%   -0.05%     
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  Lines       75988    75943      -45     
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- Hits        52570    52502      -68     
- Misses      21228    21258      +30     
+ Partials     2190     2183       -7     

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[villebro]

Good riddance! LGTM

[john-bodley]

@villebro I think this might be more nuanced than simply removing feature flags as there's no clear migration plan away from previous shared SQL Lab links which users likely perceive as somewhat persistent in nature. We (Airbnb) are discussing how best to proceed with preserving these semi-permanent URLs for a finite period.

That said, I'll be stoked when we finally remove this logic for good.

[villebro]

@john-bodley One idea that came to mind - maybe you could just introduce a new namespace into the new kv store, migrate all existing legacy links to it and add the (now to be removed) endpoint to your local app extension that serves from the new kv store? If being able to serve these ancient links post 4.0 is important that is..

[john-bodley]

@villebro I think what you proposed is similar to what I previously proposed here in relation to the removal the deprecated redirect endpoint, apart from the local app extension, i.e., having us define and manage the lifecycle of the deprecated RESTful HTTP endpoint.

[john-bodley]

@michael-s-molina note that both the KV_STORE and SHARE_QUERIES_VIA_KV_STORE feature flag is currently deemed in development as opposed to deprecated.

I'm not certain (per the Semantic Versioning wiki page) whether i) these feature flags need to be first marked as deprecated and/or if there removal is deemed a breaking change given that (per the wiki):

These features are considered unfinished and should only be used on development environments.

[michael-s-molina]

Closing in favor of #26450