feat: add files, all-files and commands as flags

[nihalgonsalves]

Closes #120

⚡ Summary

Adds --all-files, --files, and --commands to run lefthook on a subset of hooks and/or files in the repo.

New usage text:

$ lefthook run --help

Execute group of hooks

Usage:
  lefthook run hook-name [git args...] [flags]

Examples:
lefthook run pre-commit

Flags:
      --all-files          run hooks on all files
      --commands strings   run only specified commands
      --files strings      run on specified files. takes precedence over --all-files
  -h, --help               help for run
  -n, --no-tty             run hook non-interactively, disable spinner

Global Flags:
      --no-colors   disable colored output
  -v, --verbose     verbose output

☑️ Checklist

• Check locally
• Add tests
• Add documentation

I'm not sure how to add a test for these - there aren't any existing tests that operate on the cmd/run.go level and test the whole flow – how would you like that to be done?