This commit backmerges the PDF generation, enumerated headings, GitHub
Action, README notes, and other useful peripheral artifacts for
maintaining the CIM Modeling Guide via GitHub and mkdocs. The 'master'
branch had all the correct configuration that just needed to be
backmerged to the v1.1 branch.

Adds GitHub Action that you can to publish version 1.1 of the https://cim-mg.ucaiug.io
website. This isn't done autmomatically on merge but rather manually/on-demand by 
navigating to the "GitHub Action" tab of the repo and running it. This is manual so that
the CIM Modeling Guide maintainers have full control over when new versions get 
published.

The default color styling used for the PDF included red underlines and a
light grey color for hyperlinks which made them hard to see. This update
changes the red underlines to use CIM color scheme (#009dab) and changes
hyperlinks to familiar blue color.

The GitHub Action workflow for publishing the site was failing. This is
due to the gh-pages branch not getting checked out on GitHub Action
runs. It does not get checked out because by default the actions/checkout@v4
step does a very lightweight checkout (i.e. only current branch with depth
of 1). This commit adds a fetch of the gh-pages branch so that the
branch is checked out and the publish step does not report missing remote
changes.