feat(run-ginkgo): add composite action for Ginkgo test execution

[sydorovdmytro]

Summary

• Adds run-ginkgo composite action that centralizes the duplicated Ginkgo
  test execution logic from all three production repos
• Container-runtime agnostic — callers handle their own cluster and image
  setup (vind, Kind, etc.)
• Structure follows repo conventions: YAML glue only in action.yml, business
  logic in src/ scripts, bats tests in test/

Action structure

.github/actions/run-ginkgo/
  action.yml              # thin glue — validates inputs, delegates to scripts
  src/execute-tests.sh    # builds ginkgo args, handles directory/label strategy
  src/generate-summary.sh # parses JSON report into markdown failure summary
  test/
    execute-tests.bats    # 15 tests: arg construction, label filtering, flags
    generate-summary.bats # 17 tests: all states, missing report, jq errors
    fixtures/             # sample Ginkgo JSON reports

Replaces

Repo	Current approach
vcluster	.github/actions/run-ginkgo-e2e/ (local composite action)
loft-enterprise	.github/actions/run-ginkgo-e2e/ (local composite action)
vcluster-pro	Inline Ginkgo steps in e2e-next.yaml + e2e-next-nightly.yaml

Key inputs

Input	Default	Description
test-image	(required)	Image passed to the test binary
test-image-flag	--vcluster-image	CLI flag name for the image
ginkgo-label / test-dir		Mutually exclusive test selection
append-pr-label	true	Append || pr to label filter
additional-ginkgo-flags		Extra ginkgo flags (e.g. -v, --skip-package=linters)
additional-args		Extra args for the test binary

Test plan

• shellcheck clean on both scripts
• zizmor clean (0 findings) on action + test workflow
• actionlint clean (make lint)
• 32/32 bats tests pass locally (make test-run-ginkgo)
• CI green on this PR
• Migration PRs in vcluster, loft-enterprise, vcluster-pro (separate PRs after tag)