Review Standards - Change `r-jira` to `r-explain`
Created by: totten
In keeping with the discussions about JIRA, Gitlab, and issue management (e.g. https://lab.civicrm.org/infrastructure/ops/issues/817), this change would revise the "Review Standards". Instead of specifically requiring a JIRA issue for every PR, it requires a public explanation (which can be provided by JIRA, Gitlab, etc).
Note: This change tries to be the smallest reasonable alteration to the review criteria that accommodates Gitlab. However, perhaps we could make it better -- e.g. by providing examples of good and bad explanations?
Related: https://github.com/civicrm/civicrm-core/blob/master/.github/PULL_REQUEST_TEMPLATE.md