fix: Allow empty CSS in Handlebars

[michael-s-molina]

SUMMARY

Allow empty CSS in Handlebars and also add a tooltip about the required HTML sanitization when using CSS.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Screen.Recording.2022-12-14.at.5.02.02.PM.mov

TESTING INSTRUCTIONS

• You should be able to save a Handlebar without any CSS text.
• A tooltip is displayed about the required HTML sanitization when using CSS.

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

Merging #22422 (9babf44) into master (aa0cae9) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master   #22422      +/-   ##
==========================================
- Coverage   66.90%   66.89%   -0.01%     
==========================================
  Files        1850     1850              
  Lines       70677    70682       +5     
  Branches     7749     7752       +3     
==========================================
  Hits        47285    47285              
- Misses      21376    21381       +5     
  Partials     2016     2016              

Flag	Coverage Δ
javascript	53.85% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ars/src/components/ControlHeader/controlHeader.tsx	50.00% <ø> (ø)
...gin-chart-handlebars/src/plugin/controls/style.tsx	28.57% <0.00%> (ø)
...ars/src/components/Handlebars/HandlebarsViewer.tsx	0.00% <0.00%> (ø)

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[rusackas]

We might be able to inspect the config, and only show this tooltip if it's not configured properly. And perhaps not show the code editor if it's not configured properly. But that's another PR...

[rusackas]

Love it! Thank you!!!