ci: rename cron-weekly.yaml to weekly-docs.yaml (#7886)

Renames `cron-weekly.yaml` to `weekly-docs.yaml`

.github/workflows/weekly-docs.yaml

@@ -0,0 +1,32 @@
+name: weekly-docs
+# runs every monday at 9 am
+on:
+  schedule:
+    - cron: "0 9 * * 1"
+  workflow_dispatch: # allows to run manually for testing
+
+jobs:
+  check-docs:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@master
+
+      - name: Check Markdown links
+        uses: gaurav-nelson/github-action-markdown-link-check@v1
+        id: markdown-link-check
+        # checks all markdown files from /docs including all subfolders
+        with:
+          use-quiet-mode: "yes"
+          use-verbose-mode: "yes"
+          config-file: ".github/workflows/mlc_config.json"
+          folder-path: "docs/"
+          file-path: "./README.md"
+
+      - name: Send Slack notification
+        if: failure()
+        run: |
+          curl -X POST -H 'Content-type: application/json' -d '{"msg":"Broken links found in the documentation. Please check the logs at ${{ env.LOGS_URL }}"}' ${{ secrets.DOCS_LINK_SLACK_WEBHOOK }}
+          echo "Sent Slack notification"
+        env:
+          LOGS_URL: https://github.com/coder/coder/actions/runs/${{ github.run_id }}