Install only production dependencies using Bun

[neanias]

This could be extended to the other major JS providers too, but that
might be out of scope for this.

[rubys]

Cool! Possibly related: oven-sh/bun#3605

[neanias]

Oh, interesting! I wonder which is the more useful way around in this case 🤔

[neanias]

I'm not clear what's actually failing in these tests. The postgres tests seem unrelated?

[rubys]

Note that that issue is still unresolved. The desire is that the end result is that only production dependencies are installed in the final image. I'm fine if the way to achieve that result varies by packaging tool. In fact, it seems necessarily so.

As to Postgres, it looks like Rails recently changed and the test case simply needs to be updated to match: rails/rails@de9dd40 ; that need not hold up this pull request.

[neanias]

I'm happy to add some other packaging tools as part of this PR whilst I'm at it if you'd like?