ICU-23247 Create gemini code assist config file

.gemini/config.yaml

diff --git a/.gemini/config.yaml b/.gemini/config.yaml
new file mode 100644
index 0000000..ff87822
--- /dev/null
+++ b/.gemini/config.yaml
@@ -0,0 +1,13 @@
+# Copyright (C) 2026 and later: Unicode, Inc. and others.
+# License & terms of use: http://www.unicode.org/copyright.html
+
+have_fun: true
+code_review:
+  disable: false
+  comment_severity_threshold: LOW
+  max_review_comments: -1
+  pull_request_opened:
+    help: false
+    summary: false
+    code_review: false
+ignore_patterns: []