feat: add Eclipse ECA notification for PR contributors

[diogomatsubara]

Summary

This PR adds a feature to notify PR authors when they haven't signed the Eclipse Contributor Agreement (ECA).

Changes

• New workflow pr-eca-notify.yml: A reusable workflow that checks the ECA status and posts a helpful comment on the PR when ECA validation fails
• Updated pr-label-checklists-generate.yml: Added optional integration with the ECA notification workflow via the enable-eca-notify input

Features

When the ECA check fails, the workflow posts a comment that includes:

• Explanation of what the ECA is and why it's required
• Step-by-step instructions to sign the ECA
• How to verify commit email matches Eclipse account
• Links to ECA validation status, sign page, and FAQ

When the ECA is successfully signed, the comment is updated to reflect the success.

Usage

To enable ECA notification in a repository:

jobs:
  pr-checks:
    uses: eclipse-zenoh/ci/.github/workflows/pr-label-checklists-generate.yml@main
    with:
      enable-eca-notify: true
    secrets:
      github-token: ${{ secrets.GITHUB_TOKEN }}

Or use standalone:

jobs:
  eca-notify:
    uses: eclipse-zenoh/ci/.github/workflows/pr-eca-notify.yml@main
    secrets:
      github-token: ${{ secrets.GITHUB_TOKEN }}

Related

This addresses the need to help contributors like in eclipse-zenoh/zenoh#2399 who submit PRs without having signed the ECA.