I'm trying to setup an lambda function triggered by S3 events within a localstack docker-compose environment.
I've got the latest localstack image running in one service with S3, Lambda and APIGATEWAY and the second service is using `awslocal` to communicate with the localstack.

I have gotten as far as successfully creating a lambda function but when I attempt to `add-permission` I get a 404 Not Found error.

My command is:
```
awslocal lambda add-permission 
--function-name my-lambda-function 
--action lambda:InvokeFunction 
--statement-id s3 
--principal s3.amazonaws.com 
--source-arn arn:aws:s3:::event-source-bucket
```

This works against AWS so I'm not sure what I need to have setup within localstack to get it working.  Thanks for any insight you may have.
""" Get an existing event source mapping
        ---
        operationId: 'getEventSourceMapping'
        parameters:
            - name: 'request'
              in: body
    """
    mappings = event_source_mappings
    mappings = [m for m in mappings if mapping_uuid == m.get('UUID')]
    if len(mappings) == 0:
        return not_found_error()
    return jsonify(mappings[0])
@app.route('%s/event-source-mappings/' % PATH_ROOT, methods=['POST'])
def create_event_source_mapping():