.github/copilot-instructions.md: add go style guidelines (#21629)

* .github/copilot-instructions.md: add go style guidelines

Added code style guidelines and reviewer recommendations.

* remove uber to reduce context window

Author: jmank88

.github/copilot-instructions.md

@@ -18,3 +18,11 @@ Identify specific code blocks that require **scrupulous human review**. Focus on
 Analyze the `CODEOWNERS` file and the git history (recent editors) to suggest the most qualified reviewers.
 - Prioritize individuals who have made significant recent contributions to the specific files modified.
 - Cross-reference these contributors with the defined `CODEOWNERS` for the directory.
+
+### 4. Code Style
+Give style advice based on the following guides, in order of priority.
+1. [Effective Go](https://go.dev/doc/effective_go)
+2. [Google Code Review Comments](https://go.dev/wiki/CodeReviewComments)
+3. [Google Style Guide](https://google.github.io/styleguide/go/)
+
+Style exceptions are acceptable when aligning with pre-existing "local" style from the same file or package, but they should still be noted.