R1:9e65e6c50342

Support "JIRA Issue URIs" as a Herald field for revisions

Summary:
See PHI1175. An install would like to trigger some reminders/guidance if users don't link revisions to JIRA issues.

Expose "JIRA Issue URIs" as a field so Herald can act on the presence or absence of issues.

I'm exposing "JIRA Issue URIs", not a field like "[ Has Jira Issue ][ is true ]", since it's a bit more flexible: you can use a regexp to test against particular `PROJ-123` project prefixes in JIRA, for example.

Test Plan…