add basic gemini config (disable summary) (#14549)

.gemini/config.yaml

@@ -0,0 +1,9 @@
+have_fun: false
+code_review:
+  disable: false
+  comment_severity_threshold: LOW
+  max_review_comments: -1
+  pull_request_opened:
+    help: true
+    summary: false
+    code_review: true