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
```
import re
import os
import imp
import sys
import json
import uuid
import time
import base64
import logging
import threading
import traceback
import hashlib
import functools
from io import BytesIO
from datetime import datetime
from six.moves import cStringIO as StringIO
from six.moves.urllib.parse import urlparse
from flask import Flask, Response, jsonify, request
from localstack import config
from localstack.constants import TEST_AWS_ACCOUNT_ID
from localstack.services import generic_proxy