tests/service/storagegateway: Refactor to use aws_ec2_instance_type_offering and aws_ssm_parameter data sources (#12247)
tests/service/storagegateway: Refactor to use aws_ec2_instance_type_offering and aws_ssm_parameter data sources (#12247)

Reference: https://docs.aws.amazon.com/storagegateway/latest/userguide/Requirements.html
Reference: https://docs.aws.amazon.com/storagegateway/latest/userguide/ec2-gateway-file.html

Rather than manually maintain an EC2 Availability Zone blacklist for a specific instance type, we can now query EC2 to choose from available Instance Types. Also switches the AMI lookups to use the Storage Gateway documented method of AWS managed SSM Parameter values.

Output from acceptance testing:

```
--- PASS: TestAccAWSStorageGatewayGateway_CloudWatchLogs (242.70s)
--- PASS: TestAccAWSStorageGatewayGateway_GatewayName (281.47s)
--- PASS: TestAccAWSStorageGatewayGateway_GatewayTimezone (222.28s)
--- PASS: TestAccAWSStorageGatewayGateway_GatewayType_Cached (238.61s)
--- PASS: TestAccAWSStorageGatewayGateway_GatewayType_FileS3 (240.81s)
--- PASS: TestAccAWSStorageGatewayGateway_GatewayType_Stored (182.66s)
--- PASS: TestAccAWSStorageGatewayGateway_GatewayType_Vtl (227.83s)
--- PASS: TestAccAWSStorageGatewayGateway_SmbActiveDirectorySettings (725.52s)
--- PASS: TestAccAWSStorageGatewayGateway_SmbGuestPassword (238.51s)
--- PASS: TestAccAWSStorageGatewayGateway_tags (239.00s)
```
terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws