Add store unit tests and add make target for testing store with postgres (#5925)

* Add store unit tests and add make target for testing store with postgres

* Remove postgres target form test-server target

* Fix audit test

store/store.go

@@ -126,7 +126,6 @@ type ChannelStore interface {
 	PermanentDeleteMembersByUser(userId string) StoreChannel
 	PermanentDeleteMembersByChannel(channelId string) StoreChannel
 	UpdateLastViewedAt(channelIds []string, userId string) StoreChannel
-	SetLastViewedAt(channelId string, userId string, newLastViewedAt int64) StoreChannel
 	IncrementMentionCount(channelId string, userId string) StoreChannel
 	AnalyticsTypeCount(teamId string, channelType string) StoreChannel
 	ExtraUpdateByUser(userId string, time int64) StoreChannel