Fix release-plan rollout campaign for production use

[hdamker]

Problem description

The release-plan rollout campaign (#103) needs three fixes before the actual production rollout:

1. Validation action reference error: The workflow uses hdamker/tooling/shared-actions/validate-release-plan@release-plan-validation which fails with "Unable to resolve action, unable to find version release-plan-validation". Should reference camaraproject/tooling/shared-actions/validate-release-plan@v0.

2. PR body missing context: The PR templates created in target repositories should note that adding release-plan.yaml is a prerequisite for the planned release automation, but does not yet enable the automated release workflow itself.

3. No exclude filter: There is no way to exclude specific repositories from the rollout. An exclude input (comma-separated list, similar to the existing include input) is needed to skip repositories that should not receive release-plan.yaml yet.

Possible evolution

• Fix the action reference to camaraproject/tooling@v0
• Add a short note to both PR body templates (with-releases and no-releases)
• Add exclude workflow input with filtering logic in the select job

Additional context

Related to the release automation rollout tracked in camaraproject/ReleaseManagement#357.