Support shell completion via carapace spec generation

[FollowTheProcess]

Summary

Adds support for generating shell completion scripts via carapace-bin and emitting a spec with a CompletionSubCommand() function which adds a completion subcommand to your CLI

[codecov]

Codecov Report

❌ Patch coverage is 88.73239% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.29%. Comparing base (ef903fa) to head (17abee3).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
completion.go	88.73%	5 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #197      +/-   ##
==========================================
+ Coverage   85.13%   85.29%   +0.16%     
==========================================
  Files           8        9       +1     
  Lines        1507     1578      +71     
==========================================
+ Hits         1283     1346      +63     
- Misses        162      167       +5     
- Partials       62       65       +3     

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