Add gke-deploy internal IP option

[Haihan-Jiang]

Summary

• add --internal-ip to gke-deploy run and gke-deploy apply
• pass the option through the deployer/cluster credential path
• use gcloud container clusters get-credentials --internal-ip when gcloud is available
• use the GKE private endpoint when the Go client path writes kubeconfig
• add unit coverage for credential args, endpoint selection, and option propagation

Fixes #1023.

Validation

• go test ./services ./core/cluster ./deployer ./cmd/...
• go test ./...
• go run main.go apply --help | rg -- '--internal-ip|--cluster|--location'
• go run main.go run --help | rg -- '--internal-ip|--cluster|--location'
• go run main.go apply --internal-ip -f configs
• git diff --check

[Haihan-Jiang]

This is ready for review from my side. The visible checks are green; could someone take a look when convenient?