ci: add luarocks-tag-release workflow

[mrcjkb]

Summary

This PR is part of a push to get (neo)vim plugins on LuaRocks.

• See this blog post, which follows up on a series of posts by @teto.
• I'm aware this is a vimscript plugin. But that does not prevent luarocks from being able to package this :)

Things done:

• Add a workflow that publishes tags to LuaRocks when a tag is pushed.
• Add a LuaRocks badge to the readme (assuming the existence of a unblevable/quick-scope package).

Notes

• For the release workflow to work, someone with a Luarocks account will have to add their API key to this repo's GitHub actions secrets.
• Due to a shortcoming in LuaRocks (https://github.com/luarocks/luarocks-site/issues/188), the neovim label has to be added to the LuaRocks package manually (after the first upload), for this plugin to show up in https://luarocks.org/labels/neovim
• If you would prefer rolling releases without tags, this is also possible.

Adding the API key (screen shot)

[bradford-smith94]

Hey, thanks for the detailed pull request, sorry I haven't addressed it sooner if fell into my email backlog.

I don't have access to the repository settings, so for this one we'd need @unblevable to weigh in.

[unblevable]

@mrcjkb Your article has convinced me 😄

Thanks for the PR, I've added the API key. I'll add a new tag/release shortly

[mrcjkb]

Nice! Thanks for supporting us :smile: