R1:825fb9c85ae7

Add JIRA doorkeeper and remarkup support

Summary:
Ref T3687. Adds a Doorkeeper bridge for JIRA issues, plus remarkup support. In particular:

- The Asana and JIRA remarkup rules shared most of their implementation, so I refactored what I could into a base class.
- Actual bridge implementation is straightforward and similar to Asana, although probably not similar enough to really justify refactoring.

Test Plan:
- When logged in as a JIRA-connected user, pasted a JIRA issue link and saw it enriched…