chore: turn on SQLLAB_BACKEND_PERSISTENCE by default

[ktmud]

SUMMARY

#8060 has been in flight for a couple of years and no major issues reported from trail users (e.g. Preset), let's turn it default on in v2.0 as it can significantly improve the capacity of the SQL Lab tabs.

Will fix any remaining issues that may be reported by the community in 2.x.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

• SQL lab tabs should be retained after turning the flag on

ADDITIONAL INFORMATION

• Has associated issue: SIP-23: Persist SQL Lab state in the backend #8060
• 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

Merging #19107 (35ef69b) into master (51061f0) will not change coverage.
The diff coverage is n/a.

❗ Current head 35ef69b differs from pull request most recent head e9eb6a6. Consider uploading reports for the commit e9eb6a6 to get more accurate results

@@           Coverage Diff           @@
##           master   #19107   +/-   ##
=======================================
  Coverage   66.76%   66.76%           
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  Files        1670     1670           
  Lines       64392    64392           
  Branches     6499     6499           
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  Hits        42991    42991           
  Misses      19718    19718           
  Partials     1683     1683           

Flag	Coverage Δ
javascript	51.31% <ø> (ø)

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Impacted Files	Coverage Δ
...d/src/SqlLab/components/TabbedSqlEditors/index.jsx	57.53% <ø> (ø)
...rset-frontend/src/components/Checkbox/Checkbox.tsx	100.00% <ø> (ø)
...uperset-frontend/src/components/Dropdown/index.tsx	100.00% <ø> (ø)
superset/config.py	91.82% <ø> (ø)

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[ktmud]

Bycatch: fix this missing export. For some reason, this is causing Cypress test on SQL tabs to fail locally.

[ktmud]

I've rewritten the tests for SQL Lab Tabs to make them more re-runnable---so that if you have any backend persistent tabs, the tab names are still named correctly following the logics here.

cc @cccs-Dustin @kgabryje

[musicmuthu]

#21122 issue after enable the sqllab_backend_persistence