citemplate: add support for .indentignore file to indent job

See https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1465

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-ci/-/merge_requests/328>

gitlab/ci_template.yml

@@ -358,7 +358,20 @@ gst indent:
   script:
     # man indent. grep RETURN VALUE, grab a beer on my behalf...
     - indent --version || true
-    - find . -name '*.c' -exec gst-indent {} +
+    - |
+      filter_cmd="cat"
+      if test -f ".indentignore"; then
+          filter_args=""
+          while read -r line; do
+              if test -n "$line"; then
+                  filter_args="$filter_args -e $line"
+              fi
+          done < ".indentignore"
+          if test -n "$filter_args"; then
+              filter_cmd="grep -v $filter_args"
+          fi
+      fi
+      find . -name '*.c' | $filter_cmd | xargs gst-indent
     - |
       if git diff --quiet; then
           echo "Code is properly formatted"