Compose Deploy (GitHub): enhance webhook handling for registry_package event

What problem will this feature address?

Automatically triggering a deployment when a new component image is pushed requires a (potentially external) source code ref.

When triggering a compose deployment via webhook, the ref field must always be present for branch verification.
When working on workloads that live in different repositories and push Docker images to a registry, the branch check requires brittle workarounds (e.g. providing/mirroring the infra repository ref in CICD) to successfully trigger the deployment.

Describe the solution you'd like

Checks for "source code pushed" triggers are not applied to "image pushed" triggers:

• The registry_package event doesn't have to provide a branch ref (reason: sources of Images consumed do not always live in the same repository)
• Watch paths wouldn't apply to external repositories
• Docker image related metadata/checks should be sufficient

Refining both use cases and what needs to be done in which could enhance clarity and reduce configuration overhead.

Describe alternatives you've considered

Use fixed image versions and update the compose file for a release - requires additional manual effort.

Additional context

No response

Will you send a PR to implement it?

No

Start by locating the Compose Deploy webhook handling and the path for the GitHub registry_package event. Compare its required ref, branch verification, watch-path behavior, and Docker image metadata checks with source-code-pushed triggers. Done means image-pushed deployments can work without an external branch ref while source-code checks remain appropriate for their event type.