add email to user create event

internal/analytics/tracks.go

@@ -79,11 +79,14 @@ func (p segmentProperties) addAdditionalProperties(props map[string]interface{})
 // UserCreateTrackOpts are the options for creating a track when a user is created
 type UserCreateTrackOpts struct {
 	*UserScopedTrackOpts
+
+	Email string
 }
 
 // UserCreateTrack returns a track for when a user is created
 func UserCreateTrack(opts *UserCreateTrackOpts) segmentTrack {
 	additionalProps := make(map[string]interface{})
+	additionalProps["email"] = opts.Email
 
 	return getSegmentUserTrack(
 		opts.UserScopedTrackOpts,