fix: Migration for single metric in Big Number with Time Comparison

[kgabryje]

SUMMARY

Due to changing metrics control to metric in Big Number with Time Comparison chart, the existing charts were broken due to missing metric in form data. This PR adds a migration which takes the first item from metrics and applies it to the new metric control.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

1. Revert commit fd4f9ac (feat: Use standardized controls in Big Number with Time Comparison)
2. Create a Big Number with Time Comparison chart and save it
3. Un-revert the commit
4. Verify that now the chart is broken - no metric is added
5. Run the migration
6. Verify that the chart now works and metric control has a value

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
    Current: 0.13 s
    10+: 0.12 s
    100+: 0.12 s
    1000+: 0.20 s
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.72%. Comparing base (89d49e5) to head (8ef8c5a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #27351      +/-   ##
==========================================
+ Coverage   67.37%   69.72%   +2.35%     
==========================================
  Files        1908     1908              
  Lines       74550    74550              
  Branches     8317     8317              
==========================================
+ Hits        50225    51982    +1757     
+ Misses      22272    20515    -1757     
  Partials     2053     2053              

Flag	Coverage Δ
hive	53.78% <ø> (?)
javascript	57.25% <ø> (ø)
mysql	78.00% <ø> (ø)
postgres	78.10% <ø> (ø)
presto	53.73% <ø> (?)
python	83.12% <ø> (+4.88%)	⬆️
sqlite	77.62% <ø> (ø)
unit	56.50% <ø> (?)

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[mistercrunch]

We should move all to metrics and delete metric forever!

[mistercrunch]

Also - apologies - super early in the history of Superset (pre-React!) I created multiple metrics-related control instead of creating a more versatile one. I think back then it was backend generate by wtforms and they had different components for single/multiple select...

[sadpandajoe]

🏷️ preset:2024.8