chore: Add links to component issues and MRs on component page

Closes #737 (closed) (see issue for the "why").

This adds an Issues and Merge requests links in the component page footer, which links to the related component label's list of issues and merge requests on gitlab. This will help all contributors on what is currently or what is currently not being worked on when it comes to our components.

Our component labels are used for active issues and merge requests for our components, so it makes sense to link contributors to these evolving lists, rather than manually adding/removing links in Pajamas itself, or even developing something dynamic that pulls in issues to Pajamas based on a label. We already have those lists on gitlab, so it makes a lot of sense for that to be the SSOT.

I put together a couple of style options:

Option A - Link style	Option B - Button style

Final solution

Based on !2141 (comment 438595734), moving these links to the footer makes it the more appropriate place for them. The links also don't sort by milestone, as that would change the user preference locally.

Links in footer

Out of scope discoveries

I noticed trying to integrate any app-styles into the markdown requires a lot of hackery and css overriding, I'd personally like to see us just use our gitlab-ui styles completely for our documentation.