As an enhancement to https://github.com/localstack/localstack/pull/1194

It would be really helpful to send the Lambda name, either as data, a header, or as part of the URL.

At code location: https://github.com/localstack/localstack/blob/03c6f4bf250edd18eb818ed65090f508636b0bff/localstack/services/awslambda/lambda_api.py#L696

I can likely open a PR to handle this given some feedback on the feature and potential design.

Right now all I see is the following (using `npx http-echo-server`):
```
[socket#8] event: data
--> POST / HTTP/1.1
--> Host: 192.168.1.x:3000
--> User-Agent: python-requests/2.22.0
--> Accept-Encoding: gzip, deflate
--> Accept: */*
--> Connection: keep-alive
--> Content-Length: 9
--> Content-Type: application/x-www-form-urlencoded
-->
-->
[socket#8] event: data
--> Name=test
```
""" Create new event source mapping
        ---
        operationId: 'createEventSourceMapping'
        parameters:
            - name: 'request'
              in: body
    """
    data = json.loads(to_str(request.data))
    try:
        mapping = add_event_source(
            data['FunctionName'], data['EventSourceArn'], data.get('Enabled'), data.get('BatchSize')
        )
        return jsonify(mapping)
    except ValueError as error:
        error_type, message = error.args
        return error_response(message, code=400, error_type=error_type)
@app.route('%s/event-source-mappings/<mapping_uuid>' % PATH_ROOT, methods=['PUT'])
def update_event_source_mapping(mapping_uuid):