AWS: Migrate use of deprecated WithEndpointResolverWithOptions to EndpointResolverV2

[tpantelis]

Migrate this code to use EndpointResolverV2. A basic migration strategy is outlined here. It seems we might be able to set the BaseEndpoint field but we also set the PartitionID field on the aws.Endpoint and it's unclear how that maps to the new API. It's also unclear how to distinguish service names as the service name param is not passed to the EndpointResolverV2 interface.