Configure Gemini (#2298)

### What this PR does / why we need it?
This PR requests Gemini AI to review PRs.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
NA

- vLLM version: v0.10.0
- vLLM main:
vllm-project/vllm@14a5d90

Signed-off-by: QwertyJack <[email protected]>

Author: QwertyJack

.gemini/config.yaml

@@ -0,0 +1,6 @@
+# https://developers.google.com/gemini-code-assist/docs/customize-gemini-behavior-github
+have_fun: false  # Just review the code
+code_review:
+  comment_severity_threshold: HIGH  # Reduce quantity of comments
+  pull_request_opened:
+    summary: false  # Don't summarize the PR in a separate comment