Add GitLab Pages template alternative

[spswanz]

I've had some folks interested in keeping their Collection Builder site private either because it's a work in progress or they haven't sorted out usage rights yet. GitHub Pages are public (even if built from a private repo). GitLab, however, does offer access control for GitLab Pages .

[evanwill]

thanks for the suggestion @spswanz !
I have used GitLab Pages in the past, but never documented the option. There are a few things that need to be tweaked in the template for GitLab Pages. I will work on a solution for that soon, either documentation on how to get it working or maybe a mirror set up on GitLab.

[evanwill]

@spswanz I added some background and instructions to CB-Docs, https://collectionbuilder.github.io/cb-docs/docs/advanced/gitlab/

I still plan on checking if there is a way to add a template repository to GitLab or better way to share the template modifications.