fix(cli): Set exit code and shutdown signal for pending async tasks when actions are complete

[nellh]

Somewhere in a dependency the event loop is blocked preventing commands from finishing. If we reach end of execution during commands, Deno.exit should be safe to exit and set exit code 0. This also requires the upload/download actions to block until completed.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.07%. Comparing base (38da035) to head (6e5f788).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
cli/src/commands/download.ts	0.00%	8 Missing ⚠️
cli/src/commands/upload.ts	0.00%	7 Missing ⚠️
cli/mod.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3629      +/-   ##
==========================================
- Coverage   43.08%   43.07%   -0.02%     
==========================================
  Files         635      635              
  Lines       33717    33728      +11     
  Branches     1515     1515              
==========================================
  Hits        14528    14528              
- Misses      19050    19061      +11     
  Partials      139      139              

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