Add complaint_id to Complaint type

[abefernan]

The Complaint type does not include the ID, so when querying ListComplaintsResp we cannot then query specific Complaints.

complaint_id should be added to the returned response.

[maurolacy]

As an alternative, the array id in the returned Complaint array can be used as the complaint id.

For pagination, use the last array id to get the next batch. Taking care of using the absolute offset (i.e. a running counter), instead of the relative array position.

This works because the complaint ids are being auto-generated/incremented in the contract.