augment assignment logging Experiment key with allocation key (FF-848) (#27)

* handle json variant value unmarshalling correctly; add shared test files (FF-883)

* augment assignment logging Experiment key with allocation key (FF-848)

Author: leoromanovsky

eppoclient/assignmentlogger.go

@@ -8,6 +8,8 @@ type IAssignmentLogger interface {
 
 type AssignmentEvent struct {
 	Experiment        string
+	FeatureFlag       string
+	Allocation        string
 	Variation         Value
 	Subject           string
 	Timestamp         string

eppoclient/client.go

@@ -103,8 +103,11 @@ func (ec *EppoClient) getAssignment(subjectKey string, flagKey string, subjectAt
 
 	assignedVariation := variationShard.Value
 
+	// Log assignment
 	assignmentEvent := AssignmentEvent{
-		Experiment:        flagKey,
+		Experiment:        flagKey + "-" + rule.AllocationKey,
+		FeatureFlag:       flagKey,
+		Allocation:        rule.AllocationKey,
 		Variation:         assignedVariation,
 		Subject:           subjectKey,
 		Timestamp:         time.Now().String(),