Add commit hook to prevent JS from being added

[bryanmikaelian]

Description

This PR adds a commit hook that blocks adding new JS files.

Test plan

• Testing not required because this is a dev-only change

Release plan

New version is not required because it's a dev-only change

Checklist

• Thorough explanation of the issue/solution, and a link to the related issue
• CI tests are passing
• Unit tests were written for any new code
• Code coverage is at least maintained, or increased.

[nettofarah]

Love it!

[codecov-commenter]

Codecov Report

Merging #193 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #193   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines            3         3           
=========================================
  Hits             3         3           

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