rename EventConsumer => StartStopper

This more accurately defines how the interface is used. That is, the consumers
of this interface are only interested in its lifecycle functionality, that is,
Start and Stop. The fact that the implementations happen to be event
consumers, is not in any way important to the consumers themselves.

This change will require changes to the consumers however, which includes (at
least) clinic-worker, platform, hydrophone, and marketo-service. The changes
required are just function argument renaming though, so very straightforward,
and could be done the next time they upgrade their go-common versions.

events/consumer.go

@@ -2,14 +2,16 @@ package events
 
 import (
 	"context"
+	"log"
+
 	"github.com/Shopify/sarama"
 	"github.com/cloudevents/sdk-go/protocol/kafka_sarama/v2"
 	cloudevents "github.com/cloudevents/sdk-go/v2"
 	"github.com/cloudevents/sdk-go/v2/binding"
-	"log"
 )
 
-type EventConsumer interface {
+// StartStopper provides lifecycle hooks for long-running service tasks.
+type StartStopper interface {
 	Start() error
 	Stop() error
 }

events/consumer_group.go

@@ -23,7 +23,7 @@ type SaramaEventConsumer struct {
 	cancelFunc   context.CancelFunc
 }
 
-func NewSaramaConsumerGroup(config *CloudEventsConfig, consumer MessageConsumer) (EventConsumer, error) {
+func NewSaramaConsumerGroup(config *CloudEventsConfig, consumer MessageConsumer) (*SaramaEventConsumer, error) {
 	if err := validateConsumerConfig(config); err != nil {
 		return nil, err
 	}

events/fault_tolerant_consumer.go

@@ -19,14 +19,14 @@ type FaultTolerantConsumerGroup struct {
 	config         *CloudEventsConfig
 	createConsumer ConsumerFactory
 	m              sync.Mutex
-	delegate       EventConsumer
+	delegate       StartStopper
 	isShuttingDown bool
 	attempts       uint
 	delay          time.Duration
 	delayType      retry.DelayTypeFunc
 }
 
-var _ EventConsumer = &FaultTolerantConsumerGroup{}
+var _ StartStopper = &FaultTolerantConsumerGroup{}
 
 func NewFaultTolerantConsumerGroup(config *CloudEventsConfig, createConsumer ConsumerFactory) (*FaultTolerantConsumerGroup, error) {
 	return &FaultTolerantConsumerGroup{