Add extra commit metadata from `Brioche.gitCheckout`

[kylewlacy]

Follow-up to #423 (comment)

After merging #423, most packages were updated to use Brioche.gitCheckout, but some stuck with using Brioche.gitRef because they need some extra metadata. We should figure out how to provide this extra metadata even when using Brioche.gitCheckout.

Specifically, we'll need at least the following pieces of metadata:

• The git hash as a string
• The git commit date (different packages may need this in different string formats)

A few packages that need (some of) this metadata:

• caddy
• eks_node_viewer
• k9s
• popeye
• process_compose
• proot
• pstack
• yazi