Persist Monitored Validators in Config File #72
Description
Feature
If enabled persists validators in a config file so that a restart of eth-duties works without providing the validators via cli again.
Why?
This can be beneficial for large staking operators where indices are less likely being maintained manually but rather in an automated way e.g. by using eth-duties' rest api. Right now a restart forces the operator to keep track of the indices and requires some mechanism to resync. This can be avoided by some persistence feature using a read-and-write config file.