CI: Automate some GitHub PR status labels manipulations

- Set/remove "Work in Progress"/"Code Review Needed" for drafts.
 - Remove "Accepted", "Inactive", "Revision Needed" and "Stale" on
pushes and reopens.

I hope this reduce chances of PRs being forgotten after requested
modifications done due to stale labels.  It is better to have no
labels than incorrect ones saying there is nothing to look at.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #16721

.github/workflows/labels.yml

@@ -0,0 +1,49 @@
+name: labels
+
+on:
+  pull_request_target:
+    types: [ opened, synchronize, reopened, converted_to_draft, ready_for_review ]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  open:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.action == 'opened' && github.event.pull_request.draft }}
+    steps:
+      - env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          ISSUE: ${{ github.event.pull_request.html_url }}
+        run: |
+          gh pr edit $ISSUE --add-label "Status: Work in Progress"
+
+  push:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.action == 'synchronize' || github.event.action == 'reopened' }}
+    steps:
+      - env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          ISSUE: ${{ github.event.pull_request.html_url }}
+        run: |
+          gh pr edit $ISSUE --remove-label "Status: Accepted,Status: Inactive,Status: Revision Needed,Status: Stale"
+
+  draft:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.action == 'converted_to_draft' }}
+    steps:
+      - env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          ISSUE: ${{ github.event.pull_request.html_url }}
+        run: |
+          gh pr edit $ISSUE --remove-label "Status: Accepted,Status: Code Review Needed,Status: Inactive,Status: Revision Needed,Status: Stale" --add-label "Status: Work in Progress"
+
+  rfr:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.action == 'ready_for_review' }}
+    steps:
+      - env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          ISSUE: ${{ github.event.pull_request.html_url }}
+        run: |
+          gh pr edit $ISSUE --remove-label "Status: Accepted,Status: Inactive,Status: Revision Needed,Status: Stale,Status: Work in Progress" --add-label "Status: Code Review Needed"