R1:3cf17cc67f29

Herald - add field + condition for Diffusion Commits for "On autoclose branch"

Summary:
Fixes T1461.

Adds

- FIELD_ALWAYS - now you could add this to a content type to always get notified
- FIELD_REPOSITORY_AUTOCLOSE_BRANCH - solves T1461
- CONDITION_UNCONDITIONALLY - used by these two fields to not show any value for the user to select

Test Plan: made a herald rule where diffs on autoclose branches would get flagged blue. made a diff on an autoclose branch and committed it. commit was flagged!