feat: Generate shell completions on install

[jalaziz]

Homebrew can automatically generate and install completions for bash,
zsh, and fish. For now, completion is limited to bash and zsh until
graphite adds fish support.

This simplifies the installation steps for homebrew users.

[jalaziz]

@dbalatero @goldjacobe Sorry to be a pest and ping you directly, but any chance this could be reviewed?

This helps simply the graphite CLI install to a single step.

[goldjacobe]

Thanks for these PRs, I'll integrate soon (we have some other inflight changes to the release process I want to finalize first)

[goldjacobe]

this diff doesn't seem to work as expected.

[jalaziz]

@goldjacobe What issue are you seeing? No completions installed?

I had run into some issues during the last rebased, but thought I fixed everything.

I'm rebasing to test again.

[jalaziz]

@goldjacobe I just rebased and tested and it's installing the shell completions for me (I'm using zsh). Are you not seeing completions installed?

For zsh, the shell completions are installed to $(brew --prefix)/share/zsh/site-functions/_graphite. Depending on your setup, you may have to load the completions from Homebrew's completion directory: https://docs.brew.sh/Shell-Completion (not needed if you use brew installed shells)