refactor: Add new Parse Server option fileUpload.fileExtensions to restrict file upload by file extension

[mtrezza]

Fixes security vulnerability GHSA-9prm-jqwx-45x9.

[parse-github-assistant]

I will reformat the title to use the proper commit message syntax.

[parse-github-assistant]

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (db4c214) 94.32% compared to head (e40bfe5) 94.31%.

❗ Current head e40bfe5 differs from pull request most recent head 7797442. Consider uploading reports for the commit 7797442 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##            alpha    #8539      +/-   ##
==========================================
- Coverage   94.32%   94.31%   -0.01%     
==========================================
  Files         183      183              
  Lines       14550    14572      +22     
==========================================
+ Hits        13724    13744      +20     
- Misses        826      828       +2     

Impacted Files	Coverage Δ
src/Options/Definitions.js	100.00% <ø> (ø)
src/Options/index.js	100.00% <ø> (ø)
src/Config.js	91.17% <100.00%> (+0.10%)	⬆️
src/Routers/FilesRouter.js	93.33% <100.00%> (+0.81%)	⬆️

... and 2 files with indirect coverage changes

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[parseplatformorg]

🎉 This change has been released in version 6.1.0-alpha.13

[parseplatformorg]

🎉 This change has been released in version 6.3.0-beta.1

[parseplatformorg]

🎉 This change has been released in version 6.3.0-alpha.1

[parseplatformorg]

🎉 This change has been released in version 6.3.0