Improvement of Internal Structure (product- prefix in content)

This is a quality of life improvement for the maintainability of the Pajamas Design System documentation.

I know this looks like a massive MR, but it's really not. The changes in this MR are very simple:

1. All the product content sections are now prefixed with `product-". This helps a lot to differentiate the different sections since we also have brand documentation and allows us to keep a flat structure. This way is easier to map the folders to the actual content as described in the sidebar.

Another reason for this is to differentiate the product components from the actual internal components used in the documentation app. Before this change, there was a collision of naming that makes maintaining the paths/directories harder, so with the prefix is easier to understand that we are referring to the documented components.

2. This MR updates all the links in the documentation that use the old-naming to the new naming with the prefix. This is so we don't get broken links. As part of this, I also updated some links that were pointing directly to https://design.gitlab.com, instead of the relative path.