fix: add pre-release warning text, hide pre-release commands from help listing

[shazron]

1. fixed app install unzip concurrency issue

How Has This Been Tested?

• npm test
• manual tests

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.
• [X] My code follows the code style of this project.
• [X] My change requires a change to the documentation.
• [X] 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 #674 (f667ffc) into master (def82b7) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #674   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           57        57           
  Lines         3065      3072    +7     
  Branches       569       569           
=========================================
+ Hits          3065      3072    +7     

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

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