Expose release-plz release outputs to reusable workflow callers

[Teakowa]

Goal

Allow repositories using the shared release-plz-crates workflow to run repository-specific publication jobs only when release-plz actually creates a release, using the release metadata produced by that same run.

Context

The underlying release-plz/action already exposes releases and releases_created. The shared reusable workflow currently consumes those outputs internally but does not expose them to callers. Repositories that need to attach repo-specific release assets therefore cannot reliably continue the same release transaction without introducing a separate tag/release-triggered workflow or rediscovering release state.

This is a generic reusable-workflow contract; repository-specific binary build or asset publication remains owned by the caller repository.

Scope

• Expose the release creation result and release metadata needed by callers from the reusable release-plz-crates workflow.
• Preserve the existing crate publication and release-PR behavior.
• Keep the output contract generic and independent of any individual WrightKit repository.

Non-goals

• No provider/binary build logic in wrightkit/.github.
• No repository-specific asset naming or upload logic.
• No redesign of release-plz versioning or crate publication.
• No new cross-repository release orchestration service.

Acceptance criteria

• A caller can determine whether the current reusable-workflow invocation created a release.
• A caller can obtain the created release metadata needed to identify the release/tag without rediscovering it through a separate workflow trigger.
• Existing callers that do not consume the new outputs retain their current behavior.
• The reusable workflow remains repository-agnostic.