chore: rename drop missing columns to show empty columns

[zhaoyongjie]

SUMMARY

rename the control from "drop missing columns" to "show empty columns", thanks for the heads up from @stephenLYZ.

Default value is true.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

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

[stephenLYZ]

LGTM!

[codecov]

Codecov Report

Merging #20602 (ee74743) into master (309327d) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #20602   +/-   ##
=======================================
  Coverage   66.79%   66.79%           
=======================================
  Files        1754     1754           
  Lines       65565    65565           
  Branches     6935     6935           
=======================================
  Hits        43793    43793           
  Misses      20017    20017           
  Partials     1755     1755           

Flag	Coverage Δ
javascript	51.82% <100.00%> (ø)

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

Impacted Files	Coverage Δ
...t-ui-chart-controls/src/operators/pivotOperator.ts	100.00% <ø> (ø)
...controls/src/operators/timeComparePivotOperator.ts	100.00% <ø> (ø)
...t-controls/src/sections/echartsTimeSeriesQuery.tsx	50.00% <ø> (ø)
...et-ui-chart-controls/src/shared-controls/index.tsx	51.66% <100.00%> (ø)

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