[FR] Incompatible region specific endpoint error in ap-southeast-4

[tonyswu]

Is your feature request related to a problem? Please describe.
When attempting to run ecs-files-composer in ap-southeast-4 we observe the following error:

[ERROR], An error occurred (IllegalLocationConstraintException) when calling the GetObject operation: The ap-southeast-4 location constraint is incompatible for the region specific endpoint this request was sent to.

Describe the solution you'd like
We are currently working around this by supplying environment variable AWS_ENDPOINT_URL_S3=https://s3.ap-southeast-4.amazonaws.com which forces boto3 to use the endpoint specified. However I think a more integrated approach would be more preferred, i.e. a way to specify an S3 endpoint from CLI (perhaps --aws-endpoint-url-s3?), and a way to specify said S3 point in the S3 config file.

Describe alternatives you've considered
We are currently working around this by supplying environment variable AWS_ENDPOINT_URL_S3=https://s3.ap-southeast-4.amazonaws.com which forces boto3 to use the endpoint specified.