Record status of snapshot submission to relayer

[anomit]

Is your feature request related to a problem?
To complete the feature request on snapshotter implementations of Powerloom Protocol to expose an internal API for snapshot processing status per epoch PowerLoom/pooler#40, it is necessary that the payload commit service captures this information in a transient cache entry which can be parsed to generate a snapshot's status report on its state transitions.

Describe the solution you'd like
When the payload commit service of audit protocol submits a snapshot against a project ID to the relayer service, capture its success or failure from the response returned.

The proposed datamodel is as follows

type SnapshotterStateUpdate struct {
	Status    string                 `json:"status"`
	Error     string                 `json:"error"`
	Extra     map[string]interface{} `json:"extra"`
	Timestamp int64                  `json:"timestamp"`
}

This is to be recorded against the state transition of REALYER_SEND as detailed in PowerLoom/pooler#40

Describe alternatives you've considered
NA

Additional context
NA