Automate calendar files for mentoring meetings

Ah, we got rid of the main branch already. good.

I need to create an initial commit again and rebase the work I just committed without the charter commits.

mradcliffe → changed the visibility of the branch 3521850-autumate-calendar to hidden.

Success!

These files were created as artifacts that can be downloaded via from the GitLab pipeline artifacts download link. The latest artifacts shouldn't have an expiration as far as I know from reading the gitlab documentation, but I think the merge request ones will expire after the 1 week that I set in the job.

Success!

I added a custom pages job to run mkdocs and generate docs based on the mkdocs.yml file. It needed to be a custom pages job so that I could copy the calendar job artifacts into place.

The trick here is that it needs to copy the files into the docs directory somewhere, which will then get published into the public directory on build.

I had to generate an initial Gitlab pages for testing, which will be wiped out on the first build / merge, but it is available here: https://project.pages.drupalcode.org/mentoring/

I added issue links to the documentation issues as we're not ready to do anything more with GitLab pages.

I added review and manual testing instructions.