chore: Moves DropdownButton to the components folder

[michael-s-molina]

SUMMARY

Moves DropdownButton to the components folder.

This work is part of SIP-61

@rusackas @junlincc

TEST PLAN

1 - Execute all tests
2 - All tests should pass

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 #14127 (465976e) into master (a548b69) will not change coverage.
The diff coverage is n/a.

❗ Current head 465976e differs from pull request most recent head 97d95a6. Consider uploading reports for the commit 97d95a6 to get more accurate results

@@           Coverage Diff           @@
##           master   #14127   +/-   ##
=======================================
  Coverage   79.78%   79.78%           
=======================================
  Files         943      943           
  Lines       47748    47748           
  Branches     6026     6026           
=======================================
  Hits        38094    38094           
  Misses       9533     9533           
  Partials      121      121           

Flag	Coverage Δ
cypress	56.37% <ø> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
...end/src/SqlLab/components/RunQueryActionButton.tsx	64.28% <ø> (ø)
...t-frontend/src/components/DropdownButton/index.tsx	24.00% <ø> (ø)

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[rusackas]

LGTM