fix: Small tweaks for Line and Area chart migrations (ECharts)

[michael-s-molina]

SUMMARY

Fixes some issues found while testing Line and Area chart migrations (ECharts) using Airbnb's production data:

• Ensures groupby is an array. Even though the Typescript definition does not allow null values, legacy charts might have them. Check fix: Ensures form data required properties exist at runtime (echarts-timeseries) #25419 for more context about this problem.
• Adjusts the title left margin when a title is set
• Disables Y-axis zoom for stacked charts

TESTING INSTRUCTIONS

CI is sufficient as I'm already testing the migrations with a lot of data.

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-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 70.04%. Comparing base (2e5f3ed) to head (a1a1ac9).
Report is 29 commits behind head on master.

Files	Patch %	Lines
...chart-echarts/src/Timeseries/EchartsTimeseries.tsx	0.00%	2 Missing ⚠️
...gin-chart-echarts/src/Timeseries/transformProps.ts	60.00%	1 Missing and 1 partial ⚠️
...perset/migrations/shared/migrate_viz/processors.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #28334      +/-   ##
==========================================
+ Coverage   60.49%   70.04%   +9.54%     
==========================================
  Files        1931     1933       +2     
  Lines       76241    76500     +259     
  Branches     8566     8567       +1     
==========================================
+ Hits        46122    53583    +7461     
+ Misses      28015    20813    -7202     
  Partials     2104     2104              

Flag	Coverage Δ
hive	49.21% <0.00%> (+0.04%)	⬆️
javascript	57.72% <42.85%> (+<0.01%)	⬆️
mysql	77.56% <0.00%> (?)
postgres	77.67% <0.00%> (?)
presto	53.83% <0.00%> (+0.03%)	⬆️
python	83.26% <66.66%> (+19.77%)	⬆️
sqlite	77.14% <0.00%> (?)
unit	57.72% <66.66%> (+0.10%)	⬆️

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[john-bodley]

Is this just ensuring consistency with other EChart implementations?