Add s3 region into the `/temporary-table-credentials` response

[fatcloud233]

Post this comment as a separate issue: #782 (comment).

Hi @zhu-tom, what about this "region" field suggestion? Since S3 SDKs like Boto3 generally require a specific region to avoid redirection or signature issues, including it here would allow clients to initialize their S3 clients directly. This saves the caller from having to make an extra get_bucket_location or head_bucket request to resolve the region from the bucket name.

Just a detail here, we are using camelCase for TemporaryCredentials, but on Unity Catalog the model is actually snake_case: TemporaryCredentials. And also, we might need to put "region" for AWS here, since ir might be required by some SDKs.

{
  "aws_temp_credentials": {
    "access_key_id": "string",
    "secret_access_key": "string",
    "session_token": "string",
    "region": "string"
  },
  "azure_user_delegation_sas": {
    "sas_token": "string"
  },
  "gcp_oauth_token": {
    "oauth_token": "string"
  },
  "expiration_time": 0
}

Can we add region into aws_temp_credentials?

cc @dmattos-sap @zhu-tom