Update CONTRIBUTING.md with updates for proposing and drafting new Constraints and Recipes

[brendanreardon]

Feature description

GKS recently approved changes to the Technical Specification Maintenance manual, which impacts our process for proposing and drafting new Constraints and Recipes. This was discussed at the 2025-08-26 cat-vrs meeting. We should update CONTRIBUTING.md to detail and reflect these details.

As part of this, we may want to consider adding Labels to relevant Issues or Discussions to detail where new features are in this process.

Once completed, we should close the relevant Discussion.

Contribution

Yes, I can create a PR for this feature.

[DanielPuthawala]

I've made maturity-status-related labels we can add to issues and discussions. I'm not sure we need a formal PR for this, or if we can just resolve the issue as completed.

[brendanreardon]

I've made maturity-status-related labels we can add to issues and discussions.
❗ That is neat! I think that it would still be nice to briefly incorporate this into CONTRIBUTING.md. I can take ownership of doing that Pull Request in due time to see what ya'll think.

[DanielPuthawala]

Oh yea, that makes sense!