test: migrate config and group commands to ginkgo e2e - #1

Summary

• migrate plugin-config, plugin-metadata, global-rule, and consumer-group command coverage from mocked Admin API tests to real Ginkgo E2E coverage
• keep only local unit tests for CLI validation and self-contained logic
• intended as stacked helper PR on the fork because upstream base branches are not writable from the current account

Validation

• go test ./pkg/cmd/pluginconfig/... ./pkg/cmd/pluginmetadata/... ./pkg/cmd/globalrule/... ./pkg/cmd/consumergroup/...
• go test -c -tags e2e ./test/e2e
• go test -tags e2e ./test/e2e -run TestE2E -ginkgo.focus="plugin-config command" -ginkgo.v
• go test -tags e2e ./test/e2e -run TestE2E -ginkgo.focus="plugin-metadata command" -ginkgo.v
• go test -tags e2e ./test/e2e -run TestE2E -ginkgo.focus="global-rule command" -ginkgo.v
• go test -tags e2e ./test/e2e -run TestE2E -ginkgo.focus="consumer-group command" -ginkgo.v