Backport JIRA service

Fixes #3839 

Move EE JIRA functionality back to CE.

- [x] Make it function in manual testing
- [x] Migrate JIRA-specific tests
- [x] Tests pass
- [x] Migrate documentation
- [x] Rollback to previous CE JIRA integration locally, activate on a project then try to migrate db and see if integration still works.
- [x] Final EE search for JIRA references

See merge request !2146