[cicd] add initial cicd attributes to registry

[adrielp]

Adds proposed CICD common attributes to the registry.

Fixes #915

Changes

Please provide a brief description of the changes here.

Note: if the PR is touching an area that is not listed in the existing areas, or the area does not have sufficient domain experts coverage, the PR might be tagged as experts needed and move slowly until experts are identified.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

[adrielp]

This pull request comes out of #915. Notably, this comment on the issue. I additionally added the attestation attribute.

As of the time of writing this comment, this pull request does not address the filling:

• vendor extensions
• enumerated vendors (eg. db conventions)
• overarching namespace
• elaborated descriptions of each attribute. Right now referencing the original issue but will re-eval each description as questions arise.

Will be having some convo's this week & iterating as necessary.

Additionally, I noticed deployment.environment was something already defined as experimental. I've migrated this into the deployment.environment.name attribute. One thing I noticed is that deployment had its own file, so I kept the additional deployment attributes in this file.

This begs the question, should I separate out each namespace (ie. scm, pipeline, etc) into it's own file or should I conglomerate them into cicd.yaml?

[jsuereth]

Thanks for making the changes from our discussion! Looks good.

[trisch-me]

LGTM. Thanks for this huge PR and work, you have put into it.
I just left minor comments, but they are not affecting my approval