Deployment Comment: Add Details of Commit Hash For all @git Refs

[CodeGat]

Blocked by ACCESS-NRI/spack#4.

Background

Using @git.BRANCH refs means that when a package is built has an effect on the HEAD of the branch, and thus the built package. It's also quite hard to actually know which commit was used in a @git.BRANCH ref.

Implementation Plan

• In the deployment comment, add another collapsable section that displays all commit references for packages with @git. refs.
  • Consider how to get the actual commit reference of a branch ref. I suspect we would need to interrogate the low level package details via spack python

Thanks @anton-seaice !