E2E and Breeze coverage for the executable coordinator path (Go SDK) #66943

Background

breeze start-airflow --sdk go exists today, but it stands up the
Edge Worker Go path (cmd/airflow-go-edge-worker). The
coordinator path - Python @task.stub Dag dispatching to a Go bundle
via ExecutableCoordinator - has no Breeze overlay and no
airflow-e2e-tests/ coverage. The Java equivalent landed under
#65959 and is the template.

What needs to happen

1. Add a go-sdk-coordinator.yml overlay (or extend --sdk go) to
   airflow-e2e-tests/ that:
   • Builds the example Go bundle with airflow-go-pack.
   • Drops the resulting executable into the
     [executable] bundles_folder directory.
   • Configures [sdk] queue_to_sdk to route a queue to the
     executable coordinator.
2. Add test_go_sdk_coordinator.py covering both shapes:
   • Pure-Go Dag built from go-sdk/example/bundle/main.go.
   • Python stub Dag whose @task.stub(queue="go") tasks resolve to
     the Go bundle.
3. Reuse the conftest/fixture pattern set up for Java in Add CI, E2E Tests, and Pre-commit Hooks for Java SDK #65959.

Acceptance criteria

• The two test shapes run green in CI.
• A regression in ExecutableCoordinator.task_execution_cmd (such as
  the one fixed in 8612c4574f2) would have been caught by these
  tests.

Context

• Java parallel: Add CI, E2E Tests, and Pre-commit Hooks for Java SDK #65959.
• Edge-Worker quickstart that already exists: go-sdk/README.md.
• Breeze Go-worker support: commit eff66653029.

Drafted-by: Claude Code (Opus 4.7) (no human review before posting)