<!-- 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))
  }
})
```

r = s.get(url, stream=True, verify=verify_ssl)
    
    if r.status_code >= 400:
        raise Exception('Failed to download %s, response code %s' % (url, r.status_code))
    total = 0
    try:
        if not os.path.exists(os.path.dirname(path)):
            os.makedirs(os.path.dirname(path))
        LOG.debug('Starting download from %s to %s (%s bytes)' % (url, path, r.headers.get('content-length')))
        with open(path, 'wb') as f:
            for chunk in r.iter_content(DOWNLOAD_CHUNK_SIZE):
                total += len(chunk)
                if chunk:  
                    f.write(chunk)
                    LOG.debug('Writing %s bytes (total %s) to %s' % (len(chunk), total, path))
                else:
                    LOG.debug('Empty chunk %s (total %s) from %s' % (chunk, total, url))
            f.flush()
            os.fsync(f)
        if os.path.getsize(path) == 0:
            LOG.warning('Zero bytes downloaded from %s, retrying' % url)
            download(url, path, verify_ssl)
            return
        LOG.debug('Done downloading %s, response code %s, total bytes %d' % (url, r.status_code, total))
    finally:
        r.close()
        s.close()
def first_char_to_lower(s):
    return '%s%s' % (s[0].lower(), s[1:])
def is_number(s):