[WIP]: new-plugin CI workflow

[MattSturgeon]

Initial conceptual stub for a CI workflow that can announce new plugins.

Pushing this up WIP and unfinished as I find GitHub workflows particularly draining 😅

Hopefully I've stubbed enough out that someone could continue this if I eventually abandon it. 👀

[khaneliman]

Should be able to have @GaetanLepage set up a repo environment variable for this that we can reference

[MattSturgeon]

Yeah. Generating a token is documented upstream here. I guess we'd want a dedicated "bot" user?

Assuming the repo secret will be named CI_MATRIX_TOKEN for now.

[MattSturgeon]

Barring some testing and cleanup, this should be functionally complete.

I've been testing the python script (used to generate a workflow matrix, and get some other metadata) as follows:

# Test the raw data collection:
$ nix run .#ci-new-plugin-matrix -- github:nix-community/nixvim/336ba155ffcb20902b93873ad84527a833f57dc8 --head 95b322a5220744a5cac725e62fa4e612851edbc2 --raw

# Test the formatted messages produced:
$ nix run .#ci-new-plugin-matrix -- github:nix-community/nixvim/336ba155ffcb20902b93873ad84527a833f57dc8 --head 95b322a5220744a5cac725e62fa4e612851edbc2

Which appears to be working correctly.

I haven't gotten around to testing the CI workflow itself, but I have attempted to extract as much complexity as possible out of the workflow and into the python script.

As far as cleanup is concerned, it'd be nice to:

• improve the CLI interface
• comment any confusing code
• DRY up the github rest api functions

Any early feedback and/or help testing would be greatly appreciated!