fix: ACNA-2561 - app pack command should exclude hidden files

[shazron]

Currently the files to be packed are defined by npm pack --dry-run --json and exclusions are defined by the .gitignore file. However, if the app folder does not have .gitignore, certain sensitive files may still be included. This PR will exclude these files no matter what.

These files are excluded from being packed:

1. any "hidden" file by convention (file that starts with a '.')
2. any junk file as defined by https://www.npmjs.com/package/junk

How Has This Been Tested?

npm test

Types of changes

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [X] I have signed the Adobe Open Source CLA.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [X] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [X] All new and existing tests passed.

[codecov[bot]]

Codecov Report

Merging #734 (834b482) into master (abe5113) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #734   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           57        57           
  Lines         3208      3223   +15     
  Branches       605       607    +2     
=========================================
+ Hits          3208      3223   +15     

Files	Coverage Δ
src/commands/app/pack.js	100.00% <100.00%> (ø)

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