feat: add timezone selector component

[eschutho]

SUMMARY

These changes add a new component for choosing timezones client side. It uses the timezone list from moment-timezone which has about 400 entries. To narrow that list for a UI dropdown, I have removed all duplicates (based on their standard and daylight timezone offsets). There is a map that makes some of these selections more readable; for example, "America/Los_Angeles" is a duplicate of Vancouver, so we map it to "Pacific Standard/Daylight Time". In a v2 I may see if there's a simple way to pull that name out of moment, but for now, there's a map of about 7-8 regions that seem to work.
There's a migration and some changes coming next that will implement this into reports. For now these changes should have no UI impact, and just introduce the component and storybook files.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Example from storybook showing "UTC" being mapped to GMT

TESTING INSTRUCTIONS

No visual changes in Superset yet, but you can test by running storybook

ADDITIONAL INFORMATION

• Has associated issue:
• 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 #15880 (4f0348a) into master (9c854ff) will increase coverage by 0.00%.
The diff coverage is 97.77%.

@@           Coverage Diff           @@
##           master   #15880   +/-   ##
=======================================
  Coverage   77.09%   77.09%           
=======================================
  Files         984      985    +1     
  Lines       51782    51842   +60     
  Branches     7028     7067   +39     
=======================================
+ Hits        39920    39967   +47     
- Misses      11637    11650   +13     
  Partials      225      225           

Flag	Coverage Δ
javascript	71.77% <97.77%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
...frontend/src/components/TimezoneSelector/index.tsx	97.77% <97.77%> (ø)
...nd/src/explore/components/DataTablesPane/index.tsx	78.12% <0.00%> (-6.15%)	⬇️
...c/components/ErrorMessage/DatabaseErrorMessage.tsx	90.90% <0.00%> (-3.83%)	⬇️
...d/src/explore/components/PropertiesModal/index.tsx	81.94% <0.00%> (-2.35%)	⬇️
superset-frontend/src/dataMask/reducer.ts	65.38% <0.00%> (-1.93%)	⬇️
...src/explore/components/controls/ViewQueryModal.tsx	76.00% <0.00%> (-0.93%)	⬇️
...src/dashboard/components/FiltersBadge/selectors.ts	75.22% <0.00%> (-0.48%)	⬇️
...ontrols/DndColumnSelectControl/DndMetricSelect.tsx	41.04% <0.00%> (-0.44%)	⬇️
.../src/explore/components/DataTableControl/index.tsx	98.00% <0.00%> (-0.04%)	⬇️
...frontend/src/views/CRUD/alert/AlertReportModal.tsx	61.70% <0.00%> (ø)
... and 7 more

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[betodealmeida]

This looks great!