github action workflows

[Ryun1]

ideas for workflows to automate things

• workflow to check pull requests that contain CIPs/CPSs include the correct yaml header
• conformance to CIP/CPS template
• pull request description linking to rendered version

[Ryun1]

workflow to check pull requests that contain CIPs/CPSs include the correct yaml header

a workflow like validate-header.yml

runs a script like validate_markdown_header.py

[rphair]

a script like validate_markdown_header.py

and also, as per #925 (comment), impose a sort order on the YAML fields? (though personally I think it's fine to leave to author's discretion, since some fields seem to have a different "significance" in different documents)

(this comment essentially duplicates #863 (comment))