Streamline our github actions

[slifty]

Based on some recent work in the sftp-service repository it seems we can avoid the time-cost of running npm install fresh every time / we can benefit from some caching.

In general we might have some other improvements to our workflows that we should consider. This issue is a little bit broad intentionally, but ultimately the scope is "low hanging improvement fruit" which I think will become pretty obvious when doing the work.