Release Notes related to HDC 1 and 3A/3B

[qqmyers]

What this PR does / why we need it: With the interactions between HDC PRs, it makes more sense to have one integrated release notes - this is it.

Which issue(s) this PR closes:

Closes #8611

Special notes for your reviewer:

Suggestions on how to test this:

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

Is there a release notes update needed for this change?:

Additional documentation: