fix(viz): Header scrolling for Time Table in dashboard

[Antonio-RiveroMartnez]

SUMMARY

Our dashboard includes dnd.less which makes our headers fall under the sparkline when scrolling. So we Increase the z-index in order to avoid such scenario.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

BEFORE:

AFTER:

TESTING INSTRUCTIONS

1. Create a time series table
2. Add a time series column and make it a sparkline
3. Add your chart to a dashboard
4. On the dashboard, scroll the chart

Expected Results:

1. The sparklines don't overlap with the header of the table

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 #20874 (99817dc) into master (6e6d4e3) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #20874      +/-   ##
==========================================
- Coverage   66.27%   66.25%   -0.02%     
==========================================
  Files        1757     1757              
  Lines       66955    66978      +23     
  Branches     7109     7117       +8     
==========================================
+ Hits        44374    44377       +3     
- Misses      20766    20784      +18     
- Partials     1815     1817       +2     

Flag	Coverage Δ
javascript	51.91% <ø> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
...rontend/src/visualizations/TimeTable/TimeTable.jsx	0.00% <ø> (ø)
...ntrols/MetricControl/AdhocMetricPopoverTrigger.tsx	78.04% <0.00%> (-5.74%)	⬇️
...ols/MetricControl/AdhocMetricEditPopover/index.jsx	75.53% <0.00%> (-2.50%)	⬇️
...ColumnSelectControl/ColumnSelectPopoverTrigger.tsx	63.63% <0.00%> (-1.89%)	⬇️
...ols/DndColumnSelectControl/ColumnSelectPopover.tsx	3.26% <0.00%> (-0.49%)	⬇️

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[rusackas]

FWIW, this is in the LESS codebase as z-index-above-dashboard-charts but obviously we're not using LESS here. This PR seems fine, but I wonder if we should make a levels/z-index registry in our Emotion theme. @michael-s-molina @eric-briscoe we might want to have a chat about how we can clean/support/scale these layers.

[diegomedina248]

or review, most of those should not be needed at all