Release schedule updates and proposals

[Evan Zelkowitz <ez...@apache.org>]

Updates for current versions of TrafficServer and their status:

9.0 - this branch is considered dead at this point, with no changes
9.1.1 - Released
9.1.2 - In Progress
9.2 - Branched, backports are still accepted liberally

9.2 We are proposing a March 15th release date to give enough time for
fixes, testing, and the hostdb restructure.

We propose not going forward with a 9.3 as many of the remaining changes
are large such as json rpc and H2 to origin.

For 10.x we would merge 10-dev into master and then cut a 10.x branch from
master. Proposed date of June 15th for branching with a release on
September 15th.

This is what came out of our release proposal meeting. Feel free to submit
any suggestions, insight, thoughts or concerns.

- Evan