Add yamllint CI check and also run yamllint as part of `check/all`

[mhucka]

Is your feature request related to a use case or problem? Please describe.

Add a CI workflow to lint & check YAML files.

Describe the solution you'd like

Per discussions on issue #6896, this is a tracking issue to remind us to do 2 things:

• Add yamllint to the CI workflow and the check/all script
• Try if possible to auto-fix lint (perhaps using the Google tool yaml_format)

[optional] Describe alternatives/workarounds you've considered

Currently, we have a configuration file for yamllint. It needs to be invoked manually, which is not great, but better than nothing.

What is the urgency from your perspective for this issue? Is it blocking important work?

P2 - we should do it in the next couple of quarters