feat: add node reward type4 for cloud engines

[severin-amrein]

This PR adds a new node reward type type4 to the registry that will be used for Cloud Engines.

It adds tests for the following 3 scenarios since it's not yet clear how Cloud Engines will be rewarded:

1. Type4 node in a region NOT present in the rewards table -> fallback to default rewards (1 permyriad)
2. Type4 node in a region where type4 is explicitly set to 0 XDR -> 0 permyriad
3. Type4 node in a region that IS present in the rewards table -> flat per-node rewards (not type3)