golangci-lint has a v2 out, so we should eventually upgrade to it.

The main tasks here are:

1. Update the golangci-lint version in the Makefile
2. Migrate .golangci-lint.yml to the v2 configuration schema. Here is the migration guide: https://golangci-lint.run/product/migration-guide/. Unfortunately, the migration command doesn't retain comments, so please piece them back together manually after the migration (as long as the comments still make sense).
3. Address any new linting issues coming up in v2. At least in multicluster-runtime, it found one issue that needed to be fixed.