state query for single node fetches all megapool details

[jshufro]

createNetworkStateForNode is used in smart node to query the state of the network for a single node operator in many of its low-touch tasks.

However, it appears to query the state for every single node's megapool details:

smartnode/shared/services/state/network-state.go

Line 478 in 914f463

state.MegapoolValidatorGlobalIndex, err = rpstate.GetAllMegapoolValidators(m.rp, contracts)

This causes a large amount of wasted work in the rocketpool_node daemon.

The code is also not particularly DRY. I recommend refactoring so that createNetworkStateForNode and createNetworkState share an implementation, and pass through an optional list of nodes for which to query the state (empty or nil list means all)