ADD Request access links for catalog items

[jelletreep]

We can make our catalog items available upon request (i have already done this for python workbench items). We can add the link to the catalog item page in the portal to the workspace overview on our documentation page, so the users can request access directly.

[dometto]

This is a cool idea! However, I was not immediately sure how to implement it, because for some items listed in the workspace overview, we have multiple variants ('Python Workbench CLI', 'Python Workbench CUDA Desktop', etc). So which catalog item do we link to in the overview, exactly? Or would it be better to link to all catalog items on the specific page for each workspace type?

For now, I've added a simple tutorial on how to request access in #52