[ci] Add local lint setup with pre-push hook to catch issues early (#4925)

* Add local lint setup with pre-push hook to catch issues early

Developers can now catch lint issues before pushing, reducing CI failures
and iteration time. The setup uses golangci-lint locally with the same
configuration as CI.

Setup:
- Run `make setup-hooks` once after cloning
- Pre-push hook automatically lints changed files (~90s)
- Use `make lint` to manually check changed files
- Use `make lint-all` to run full CI-equivalent lint

The Makefile auto-installs golangci-lint to ./bin/ using go install to
match the Go version in go.mod, avoiding version compatibility issues.

---------

Co-authored-by: mlsmaycon <mlsmaycon@gmail.com>

CONTRIBUTING.md

@@ -136,6 +136,14 @@ checked out and set up:
    go mod tidy
    ```
 
+6. Configure Git hooks for automatic linting:
+
+   ```bash
+   make setup-hooks
+   ```
+
+   This will configure Git to run linting automatically before each push, helping catch issues early.
+
 ### Dev Container Support
 
 If you prefer using a dev container for development, NetBird now includes support for dev containers.