google gemini: Add initial configuration for code review integration (#2117)

Co-authored-by: Adrian Gallagher <adrian.gallagher@example.com>

.gemini/config.yaml

@@ -0,0 +1,13 @@
+have_fun: false
+memory_config:
+  disabled: false
+code_review:
+  disable: false
+  comment_severity_threshold: MEDIUM
+  max_review_comments: -1
+  pull_request_opened:
+    help: false
+    summary: false # Copilot already handles this
+    code_review: true
+    include_drafts: true
+ignore_patterns: []