Reorganize platform support documentation and add Harmonic

[azeey]

This consolidates all the platform support documentation into the releases page. I thought it would be better to see all the support information in one page much like REP 2000. @j-rivero we can expand on this to add more documentation on dependency requirements.

This also adds the list of platforms we plan to support in Harmonic. Per our discussion this week, Focal will not be supported in Harmonic.