### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

It seems like whenever I open a connection to `localhost:4566` (4566 being exposed from the localstack container), for the next ~1 second any HTTP calls will have delayed responses. If I open 10 connections, the delay will be 10 seconds.

### Expected Behavior

Multiple connections can be opened and don't impact other requests until a certain connection limit.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

1. run localstack: `docker run --rm -it -p 4566:4566 --name ls localstack/localstack:0.14.0` - I managed to reproduce it with versions as old as 0.12.0
2. run something like this to see how long curls take inside the container: 

```bash
docker exec -it ls /bin/bash

# inside the container:
while true; do time curl localhost:4566; sleep 0.1; done
```

3. open connections with telnet:

```
telnet localhost 4566
```

4. observe extended response times in the curl loop. For me it's ~1s extra per open connection (I'm simulating opening more connections with a JVM application opening sockets as I request).

### Environment

```markdown
- OS: macOS / ubuntu, tried both x86 and arm64 macs, and an arm64 linux
- LocalStack: 0.12.0, 0.13.1, 0.14.0
```


### Anything else?

This surfaces itself as extremely slow responses whenever you have e.g. a JVM application that keeps a cached connection pool. Even 10 connections in a pool are enough to cause consistent delays every couple seconds (which I think is after the connections are closed due to the defaults on my client), under no additional traffic targeting localstack.
self,
        method: str,
        path: str,
        data: MessagePayload,
        headers: Headers,
        response: Response,
    ) -> Optional[Response]:
        """This interceptor method is called by the proxy when returning a response
        (*after* having forwarded the request and received a response from the backend
        service). It receives details of the incoming request as well as the response
        from the backend service, and returns either of the following results:
        * An instance of requests.models.Response to return to the client instead of the
          actual response returned from the backend service.
        * Any other value, in which case the response from the backend service is
          returned to the client.
        """
        return None
    def get_forward_url(self, method: str, path: str, data, headers):
        """Return a custom URL to forward the given request to. If a falsy value is returned,
        then the default URL will be used.
        """
        return None
class MessageModifyingProxyListener(ProxyListener):