Add subprojects

[So-Fras]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? Documentation update

What is the current behavior? Only 3 subprojects are linked in the parent documentation page

What is the new behavior (if this is a feature change)? Other projects are added to the list of subprojects.

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [x] No

Other information: Some links may not be fully functional yet.

[annetill]

Thanks a lot, @olperr1 will review the release part later. My only remark could be the "releaseTrainDependencies.png" that could be more "modern" (maybe the color is because of my browser).

To be done in a later PR.