restructure cache handling, code cleanups

provider/notification-gc/pom.xml

...up/osdu/notification/provider/gcp/config/CacheConfig.java

...ion/provider/gcp/config/ExternalSubscriptionsManager.java

...sdu/notification/provider/gcp/config/RedisProperties.java

...tification/provider/gcp/config/SubscriptionCacheRepo.java

...otification/provider/gcp/model/ExternalSubscriptions.java

...n/provider/gcp/pubsub/OqmNotificationDeliveryService.java

...otification/provider/gcp/pubsub/OqmSubscriberManager.java

...ification/provider/gcp/pubsub/OqmSubscriptionHandler.java

...tion/provider/gcp/pubsub/receiver/OqmEventReplicator.java

...vider/gcp/pubsub/receiver/OqmReplicatedEventReceiver.java

...pubsub/receiver/OqmSubscriptionConfigurationReceiver.java

...notification-gc/src/main/resources/application.properties

...ification/provider/gcp/pubsub/OqmEventReplicatorTest.java

...n/provider/gcp/pubsub/OqmReplicatedEventReceiverTest.java

...ication/provider/gcp/pubsub/OqmSubscriberManagerTest.java

.../gcp/pubsub/OqmSubscriptionConfigurationReceiverTest.java