`aws-sdk-go` package name doesn't match service ID

[RedbackThomson]

Describe the bug
Each service has a ServiceID which identifies the model package directory (under aws-sdk-go/models/apis/). Each service also has a service package name used for importing the aws-sdk-go types and methods. The code currently assumes that these two are identical, as they have been for each of the controllers so far. This assumption breaks when generating the opensearchservice controller, as the model is located under /aws-sdk-go/models/apis/opensearch/ but each of the imports is github.com/aws/aws-sdk-go/service/opensearchservice

Steps to reproduce

• Run the latest version of the code-generator against the opensearchservice controller

Expected outcome

• The code-generator should load the APIs from the correct model package directory
• All types should import using the aws-sdk-go package name

Environment

• AWS service targeted (S3, RDS, etc.) opensearchservice