Add "Needs Triage" label to new PRs

@singingwolfboy god I hope this is the last thing I've overlooked.
I suck at reading API doc apparently! sheesh. Um, what is "push access" and does the bot have it? Because remember how when you log in as edx-jira there's no "Merge" button? So perhaps edx-jira doesn't have push access, and that's why closing the PR from JIRA is failing, and would also mean changing these labels will fail.