feat(annotations): Update annotations UI to display label as tooltip on hover

[kgopal492]

SUMMARY

• Update annotation UI to show tooltip on hover rather than using label to improve readability.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before

After

TESTING INSTRUCTIONS

Add annotation layer to chart, and view.

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 15.78947% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 56.33%. Comparing base (6e4d1f5) to head (91c3c8e).

Files	Patch %	Lines
...ugins/plugin-chart-echarts/src/utils/annotation.ts	0.00%	10 Missing ⚠️
...lugin-chart-echarts/src/Timeseries/transformers.ts	0.00%	2 Missing ⚠️
superset/initialization/__init__.py	33.33%	2 Missing ⚠️
superset/models/core.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           pinterest-release-2.1      #27      +/-   ##
=========================================================
- Coverage                  56.34%   56.33%   -0.01%     
=========================================================
  Files                       1886     1886              
  Lines                      72718    72729      +11     
  Branches                    7891     7893       +2     
=========================================================
  Hits                       40973    40973              
- Misses                     29722    29733      +11     
  Partials                    2023     2023              

Flag	Coverage Δ
javascript	53.88% <0.00%> (-0.02%)	⬇️
presto	52.66% <42.85%> (ø)
python	58.96% <42.85%> (ø)
unit	52.50% <14.28%> (ø)

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