Make `network` a parameter for blockchain-based credentials

[0xjei]

Description

Currently the network is derived from the url value passed to the parameter of the getJsonRpcProvider(<url>) function. With the introduction of logical operators (#223) and more complex credential scenarios, it is necessary to specify one or more networks (also custom) for the credentials.

hint: this could be something similar as done for EAS credentials.

The idea is to attach a network to every blockchain validator when creating the group so that the network always remains the same.