Lock issues and pulls faster (#29436)

also point to the docs to explain why we do so

followup to  #29433

Author: 6543

.github/workflows/cron-lock.yml

@@ -19,4 +19,9 @@ jobs:
     steps:
       - uses: dessant/lock-threads@v5
         with:
-          issue-inactive-days: 45
+          issue-inactive-days: 10
+          issue-comment: |
+            Automatically locked because of our [CONTRIBUTING guidelines](https://github.com/go-gitea/gitea/blob/main/CONTRIBUTING.md#issue-locking)
+          pr-inactive-days: 7
+          pr-comment: |
+            Automatically locked because of our [CONTRIBUTING guidelines](https://github.com/go-gitea/gitea/blob/main/CONTRIBUTING.md#issue-locking)