Add a method to call Runtime Storage and retrieve the genesis slot number.
Add a method to set the genesis slot number in EpochState. The provided value may be null, indicating that the chain has no executed blocks, in which case the current slot number is used as the genesis slot number.
Add an isInitialized flag to EpochState, which is set to TRUE only when the goal is to run an authoring node.
Description
Fixes: https://github.com/LimeChain/Fruzhin/issues/593