[feature] shell completions for shellcheck --<TAB>

[Freed-Wu]

For new checks and feature suggestions

• https://www.shellcheck.net/ (i.e. the latest commit) currently gives no useful warnings about this
• I searched through https://github.com/koalaman/shellcheck/issues and didn't find anything related

Currently completion scripts is written by people, not generated automatically.

Here's what I wanted to see:

shellcheck --completion={bash,zsh,fish} to generate completion scripts

An example is jgm/pandoc#11818 also written in haskell.

Same issues:

• Shell completions sharkdp/vivid#86
• Shell completions sharkdp/hexyl#155
• [feature] more shell completions jgm/pandoc#8542
• cmd/shfmt: add shell auto-complete mvdan/sh#914
• [feature] shell completion rhysd/actionlint#300