[Dynamic Protocol State | M1] State machine for processing KV store updates

[durkmurder]

Context

To evolve the key-value store we rely on a similar concept to what we use for processing epochs as part of Dynamic Protocol State. As mentioned in the design doc we will introduce a dedicated interface for the processing KV store state machine.

Implementation of this interface must process updates using new service events and update fields that are present in the store. New service events can be added in this issue as well.

Definition of done

• Add new service events to update fields in the KV store
• Implement a dedicated interface for mutating KV store
• Add an implementation that consumes service events and mutates KV store
• Add test suite
• Add godoc documentation