Add stale GitHub action, as replacement for old stale GitHub integration

Previously we had the "stale bot" which posted reminders in inactive
issues and PR's. The stale bot used now removed functionality of GitHub
and it hasn't worked for about a year. This commit introduces the same
functionality based on GitHub Actions. The action setup is grabbed from
the QGIS project and adapted to the PROJ project.

With the stale action in place, PR's and issues are marked "stale" after
60 days of inactivity. If 7 more days passes without any activity the
issue or PR is closed.

Author: kbevers

.github/stale.yml

@@ -0,0 +1,93 @@
+name: Handle stale issues
+on:
+  schedule:
+  - cron: "30 2 * * *"
+
+permissions:
+  contents: read
+
+jobs:
+  stale:
+    permissions:
+      issues: write  # for actions/stale to close stale issues
+      pull-requests: write  # for actions/stale to close stale PRs
+    if: github.repository_owner == 'osgeo'
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/stale@v8
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        stale-pr-message: >
+          The PROJ project highly values your contribution and would love to see
+          this work merged!
+          Unfortunately this PR has not had any activity in the last 14 days and
+          is being automatically marked as "stale".
+          If you think this pull request should be merged, please check
+
+          - that all unit tests are passing
+
+          - that all comments by reviewers have been addressed
+
+          - that there is enough information for reviewers, in particular
+
+            - link to any issues which this pull request fixes
+
+            - add a description of workflows which this pull request fixes
+
+            - add terminal output examples if applicable
+
+          - that you have written unit tests where possible
+
+          In case you should have any uncertainty, please leave a comment and we will
+          be happy to help you proceed with this pull request.
+
+          If there is no further activity on this pull request, it will be closed in a
+          week.
+
+
+        close-pr-message: >
+          While we hate to see this happen, this PR has been automatically closed because
+          it has not had any activity in the last 2 months. If this pull request should be
+          reconsidered, please follow the guidelines in the previous comment and reopen
+          this pull request. Or, if you have any further questions, just ask! We love to
+          help, and if there's anything the PROJ project can do to help push this PR forward
+          please let us know how we can assist.
+
+
+        stale-pr-label: 'stale'
+        exempt-pr-labels: 'pinned'
+        days-before-pr-stale: 60
+        days-before-pr-close: 7
+
+        stale-issue-message: >
+          The PROJ project highly values your report and would love to see it addressed.
+          However, this issue has been left in feedback mode for the last two months and is
+          being automatically marked as "stale".
+
+          If you would like to continue with this issue, please provide any missing information
+          or answer any open questions. If you could resolve the issue yourself meanwhile,
+          please leave a note for future readers with the same problem and close the issue.
+
+          In case you should have any uncertainty, please leave a comment and we will be
+          happy to help you proceed with this issue.
+
+          If there is no further activity on this issue, it will be closed in a week.
+
+
+        close-issue-message: >
+          While we hate to see this happen, this issue has been automatically closed because
+          it has not had any activity in the last two months despite being marked as feedback.
+          If this issue should be reconsidered, please follow the guidelines in the previous
+          comment and reopen this issue.
+
+          Or, if you have any further questions, there are also
+          [further support channels](https://proj.org/community/channels.html)
+          that can help you.
+
+
+        stale-issue-label: 'stale'
+        only-issue-labels: 'feedback'
+        days-before-issue-stale: 60
+        days-before-issue-close: 7
+
+        operations-per-run: 1000