Add config caching and transferring + minor fixes and changes

[lainets]

Description

What?

Adds config caching for the different build stages and transferring the configs between them to speed up the build process. Also means that the separate processes do not need to load the configs separately.

Fixes a bug with HOME variable missing in git calls.

Also contains some smaller fixes and architectural changes.

Why?

Speed up the build process.

HOME variable is needed for git to find the config files.

How?

Store the configs in a Django cache where each build stage is cached separately. Transfer the configs in the cache when the configs are transferred in the fiesystem. This eliminates the need to reload the config after each build stage.

Fixes #1. Fixes #2.

Testing

What type of test did you run?

• [ ] Accessibility test using the WAVE extension.
• [ ] Django unit tests.
• [ ] Selenium tests.
• [ ] Other test. (Add a description below)
• [X] Manual testing.

Tested that there are no difference between the config loaded from the filesystem and the config fetched from the cache on a couple courses. Should be no problems.

Did you test the changes in

• [ ] Chrome
• [ ] Firefox
• [X] This pull request cannot be tested in the browser.

Programming style

• [X] Did you follow our style guides?
• [X] Did you use Python type hinting in all functions that you added or edited? (type hints for function parameters and return values)

Have you updated the README or other relevant documentation?

• [ ] documents inside the doc directory.
• [X] README.md.
• [ ] Aplus Manual.
• [ ] Other documentation (mention below which documentation).

Is it Done?

• [ ] Reviewer has finished the code review
• [ ] After the review, the developer has made changes accordingly
• [ ] Customer/Teacher has accepted the implementation of the feature