Automatically remove obsolete labels from OSPRs upon merge/close

[itsjeyd]

Epic

#134: Improving OSPR Management

Story

"As an OSPR manager, I want obsolete labels to automatically disappear from OSPRs upon merge/close, so that I don't have to remove them manually."

Full description

See Automating manual OSPR management tasks > Managing labels section of the proposal for Improving OSPR Management from this year's Summit to Enhance the Core Contributor Experience for details:

The OSPR management process involves a number of tasks that OSPR managers currently perform manually, and that could be automated to free up time for processing more PRs in the time that OSPR managers have available for triage. These tasks include:

<...>

• Removing obsolete labels when a PR gets merged:
  • blocked by other work
  • changes requested
  • inactive
  • needs maintainer attention
  • needs more product information
  • needs rescoping
  • needs reviewer assigned
  • needs test run
  • waiting for eng review
  • waiting on author
• Removing obsolete labels when a PR gets closed:
  • needs maintainer attention
  • needs reviewer assigned
  • needs test run
  • waiting for eng review
  • waiting on author

Completion criteria

• Implement support for automatically removing obsolete labels from OSPRs as described above.
• If the code for this feature will live in the https://github.com/openedx/openedx-webhooks repo (TBC as part of this ticket), ping Feanil for review on the PR(s) that you create. (Most likely, he will take care of testing and deploying the changes once they merge.)

Relevant repositories

• https://github.com/openedx/openedx-webhooks
• Maybe others (?)