Add support for powershell completions

[sambhav]

Summary

Adds support for powershell completions

Output

Before

$ pack completion --shell powershell
ERROR: powershell is unsupported shell

$ pack completion --help

Generates completion script and outputs its location.

To configure your bash shell to load completions for each session, add the following to your '.bashrc' or '.bash_profile':

	. $(pack completion)

To configure your fish shell to load completions for each session, add the following to your '~/.config/fish/config.fish':

	source (pack completion --shell fish)

To configure your zsh shell to load completions for each session, add the following to your '.zshrc':

	. $(pack completion --shell zsh)

Usage:
  pack completion [flags]

Flags:
  -h, --help           help for completion
  -s, --shell string   Generates completion file for [bash|fish|zsh] (default "bash")

Global Flags:
      --no-color     Disable color output
  -q, --quiet        Show less output
      --timestamps   Enable timestamps in output
  -v, --verbose      Show more output

After

$ pack completion --shell powershell
/home/sam/.pack/completion.ps1

$ pack completion --help

Generates completion script and outputs its location.

To configure your bash shell to load completions for each session, add the following to your '.bashrc' or '.bash_profile':

	. $(pack completion)

To configure your fish shell to load completions for each session, add the following to your '~/.config/fish/config.fish':

	source (pack completion --shell fish)

To configure your powershell to load completions for each session, add the following to your '$PSHOME\Profile.ps1':

	. $(pack completion --shell powershell)

To configure your zsh shell to load completions for each session, add the following to your '.zshrc':

	. $(pack completion --shell zsh)

Usage:
  pack completion [flags]

Flags:
  -h, --help           help for completion
  -s, --shell string   Generates completion file for [bash|fish|powershell|zsh] (default "bash")

Global Flags:
      --no-color     Disable color output
  -q, --quiet        Show less output
      --timestamps   Enable timestamps in output
  -v, --verbose      Show more output

Documentation

• Should this change be documented?
  • Yes, see #___
  • No

Related

Resolves #976

[codecov]

Codecov Report

Merging #1094 (14c8aff) into main (89e9f4a) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1094      +/-   ##
==========================================
+ Coverage   80.36%   80.38%   +0.03%     
==========================================
  Files         133      133              
  Lines        8160     8170      +10     
==========================================
+ Hits         6557     6567      +10     
  Misses       1174     1174              
  Partials      429      429              

Flag	Coverage Δ
os_linux	79.78% <100.00%> (+0.06%)	⬆️
os_macos	?
os_windows	80.30% <100.00%> (+0.03%)	⬆️
unit	79.78% <100.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[dwillist]

Hey @samj1912 thanks! This looks & works perfectly. One small nitpick but we can make this small change before merging.