feat: luarocks support

[mrcjkb]

Hey :wave:

Summary

This PR is part of a push to get neovim plugins on LuaRocks.

• See this blog post, which follows up on a series of posts by @teto.
• See also: rocks.nvim, a new luarocks-based plugin manager.

Things done:

• Add a workflow that publishes tags to LuaRocks when a tag or release is pushed.
• This is based on the approach implemented for neotest, which should work with the existing semantic release workflow.

Notes:

• Tagged releases are installed locally and then published to luarocks.org. On PRs, a test release is installed, but not published.
• For the luarocks workflow to work, someone with a luarocks.org 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 (and other) labels have to be added to the LuaRocks package manually (after the first upload), for this plugin to show up in https://luarocks.org/labels/neovim.

[mrcjkb]

Added to the NURR.