Add workflow for Just / Make

[spwoodcock]

Instead of writing a Github specific workflow for each task, why not:

• Write all logic in Just / Make.
• Have a simple GH workflow to run any arbitrary Just / Make command.
• Replace most workflows with the same workflow, but different commands.

This way we are more platform agnostic, plus it's easier to test CI locally.

Workflow Steps

1. Checkout code
2. Copy all secrets to env like this https://github.com/oNaiPs/secrets-to-env-action then also write env to a .env file.
3. Install Just.
4. Run just xxx allowing any command to be used.

Note

We should probably have the docker build workflows as an exception as they have caching and multi arch support built in (hard to replicate).