Update docscheck.sh to accept provider function docs (#17497)

This script is a good candidate for being replaced with official tools, but for now updating this script to avoid false alarms about bad docs

scripts/docscheck.sh

@@ -27,6 +27,15 @@ for doc in $docs; do
       fi
       ;;
 
+    "functions")
+      # Functions require a page_title
+      grep "^page_title: " "$doc" > /dev/null
+      if [[ "$?" == "1" ]]; then
+        echo "Doc is missing a page_title: $doc"
+        error=true
+      fi
+      ;;
+
     *)
       error=true
       echo "Unknown category \"$category\". " \