Dedup calls to LoadConfig

[jshufro]

We often call cliutils.PrintNetwork(rp), which in turn calls rp.LoadConfig(), which then discards the result before it returns. The same functions often proceed to call rp.LoadConfig() again.

This isn't ideal for two reasons:

1. If LoadConfig ever has side-effects, it may not be reentrant
2. We parse stuff twice, which isn't slow but it isn't fast either.

Instead we can just add a function on RocketPoolConfig to get the network, and change cliutils.PrintNetwork to take that as an argument.

[0xfornax]

LGTM