Add CodeRabbit configuration to scope automated PR reviews

[karthikvetrivel]

Description

I added a .coderabbit.yaml so that CodeRabbit reviews this repo usefully.

Two things about this repo would make a default install noisy.

• Roughly half of all pull requests are machine generated by Dependabot, Renovate, and the cherry-pick workflow.
• Vendored and generated files also make up about 90% of tracked files.

The config addresses both:

• It uses the quiet profile, so only critical and major findings are posted inline.
• It skips pull requests authored by dependabot[bot] and github-actions[bot]. A backport only replays commits that were already reviewed on main.
• It filters vendor/, generated deepcopy and clientset code, the CRD copies that make sync-crds produces, and the intentionally malformed fixtures under testdata/.
• It disables golangci-lint, which CI already runs with our own config, and yamllint, which cannot parse our Helm and Go templates.

Checklist

• No secrets, sensitive information, or unrelated changes
• Lint checks passing (make lint)
• Generated assets in-sync (make validate-generated-assets)
• Go mod artifacts in-sync (make validate-modules)
• Test cases are added for new code paths

Testing

This change adds no Go code, so there are no new code paths to cover and no Go artifacts to regenerate.

[rajathagasthya]

Added some suggestions.