<!-- Love localstack? Please consider supporting our collective:
👉  https://opencollective.com/localstack/donate -->

# Type of request: This is a ...

[x ] bug report
[ ] feature request

# Detailed description

Not able to use the edge service to write metric data to cloudwatch via the javascript aws-sdk.

However, It **DOES** work when using the deprecated cloudwatch port.

## Expected behavior

Metric data to be visible when calling `awslocal cloudwatch list-metrics`

## Actual behavior

404 from edge service. No metric data is persisted, localstack instance logs the following info:

```
INFO:localstack.services.edge: Unable to determine forwarding port for API "monitoring" - please make sure this API is enabled via the SERVICES configuration
```

# Steps to reproduce

Run JS code in "Client code" section.
See 404 Error

## Command used to start LocalStack

`TMPDIR=/tmp/localstack docker-compose up`

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)

```js
const AWS = require('aws-sdk')
const cw = new AWS.CloudWatch({
  endpoint: 'http://localhost:4566',
})

const data = {
  Namespace: 'ns',
  MetricData: [
    {
      MetricName: 'metric-name',
      Timestamp: new Date(),
      Value: 12345,
      Unit: 'Milliseconds',
      Dimensions: [
        { Name: 'Environment', Value: 'local' },
      ]
    }
  ]
}

cw.putMetricData(data, (err, data) => {
  if (err) {
      console.log('Error', err)
  } else {
      console.log('Success', JSON.stringify(data))
  }
})
```

return not_found_error(arn)
    for tag_key in tag_keys:
        func_details.tags.pop(tag_key, None)
    return jsonify({})
@app.route('/2019-09-25/functions/<function>/event-invoke-config', methods=['PUT'])
def put_function_event_invoke_config(function):
    """ Updates the configuration for asynchronous invocation for a function
        ---
        operationId: PutFunctionEventInvokeConfig
        parameters:
            - name: 'function'
              in: path
            - name: 'qualifier'
              in: path
            - name: 'request'
              in: body
    """
    data = json.loads(to_str(request.data))
    function_arn = func_arn(function)
    lambda_obj = arn_to_lambda[function_arn]
    response = lambda_obj.put_function_event_invoke_config(data)
    return jsonify({
        'LastModified': response.last_modified,
        'FunctionArn': str(function_arn),
        'MaximumRetryAttempts': response.max_retry_attempts,
        'MaximumEventAgeInSeconds': response.max_event_age,
        'DestinationConfig': {
            'OnSuccess': {
                'Destination': str(response.on_successful_invocation)
            },