Adding Generate PR Description workflow (#18)

This adds a PR comment-triggered workflow that uses the action [mkarle/skonsole-generate-pr-description](https://github.com/mkarle/skonsole-generate-pr-description).  That action uses [mkarle/pr-update](https://github.com/mkarle/pr-update) to update the PR.
To use, create a comment on a PR with:
`/sk generate-pr-description <suffix(default) | prefix | replace>`
Since it's triggered from a pull request comment, it only runs if it's in the default branch of the repo. [See this PR for an example of it working.](mkarle#4)

You'll need to add the following environment variables to the repo:
- variable: AZURE_OPENAI_CHAT_DEPLOYMENT_NAME
- secret: AZURE_OPENAI_API_ENDPOINT
- secret: AZURE_OPENAI_API_KEY

.github/workflows/generate-pr-description.yml

@@ -0,0 +1,60 @@
+name: Generate PR Description
+
+# Usage: Comment on a pull request with "/sk generate-pr-description <suffix(default) | prefix | replace>"
+
+on:
+  issue_comment:
+    types: [created]
+
+jobs:
+  generate-pr-description:
+    runs-on: ubuntu-latest
+    if: github.event.issue.pull_request && contains(github.event.comment.body, '/sk generate-pr-description')
+    steps:
+      - name: Get PR branch
+        uses: xt0rted/pull-request-comment-branch@v1
+        id: comment-branch
+
+      - name: Set latest commit status as pending
+        uses: myrotvorets/set-commit-status-action@master
+        with:
+          sha: ${{ steps.comment-branch.outputs.head_sha }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+          status: pending
+
+      - name: Generate PR description
+        uses: mkarle/skonsole-generate-pr-description@v1
+        with:
+          pull-request-number: ${{ github.event.issue.number }}
+          pull-request-diff-url: ${{ github.event.issue.pull_request.diff_url }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+          update-type:  ${{ contains(github.event.comment.body, 'replace') && 'replace' || (contains(github.event.comment.body, 'prefix') && 'prefix' || 'suffix') }}
+        env: # Set Azure credentials secret as an input
+          AZURE_OPENAI_CHAT_DEPLOYMENT_NAME: ${{ vars.AZURE_OPENAI_CHAT_DEPLOYMENT_NAME }}
+          AZURE_OPENAI_API_ENDPOINT: ${{ secrets.AZURE_OPENAI_API_ENDPOINT }}
+          AZURE_OPENAI_API_KEY: ${{ secrets.AZURE_OPENAI_API_KEY }}
+
+      - name: Set latest commit status as ${{ job.status }}
+        uses: myrotvorets/set-commit-status-action@master
+        if: always()
+        with:
+          sha: ${{ steps.comment-branch.outputs.head_sha }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+          status: ${{ job.status }}
+
+      - name: Add comment to PR
+        uses: actions/github-script@v6
+        if: always()
+        with:
+          script: |
+            const name = '${{ github.workflow   }}';
+            const url = '${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}';
+            const success = '${{ job.status }}' === 'success';
+            const body = `${name}: ${success ? 'succeeded ✅' : 'failed ❌'}\n${url}`;
+
+            await github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: body
+            })