### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

There appears to be an issue with this variable `export LAMBDA_KEEPALIVE_MS=1337`.
It's not picked up when you start `localstack start -d`

```shell
$ export LAMBDA_KEEPALIVE_MS=1000
$ env | grep LAMBDA_KEEPALIVE_MS
LAMBDA_KEEPALIVE_MS=1000
$ localstack start -d
$ docker inspect localstack_main -f '{{json .Config.Env}}' | grep LAMBDA_KEEPALIVE_MS
```

### Expected Behavior

It should be set in the container environment.

### How are you starting LocalStack?

With the `localstack` script

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

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

    awslocal s3 mb s3://mybucket


### Environment

```markdown
- OS: Windows (WSL)
- LocalStack: 2.2.1.dev20230731233910
```


### Anything else?

_No response_
if not isinstance(other, self.__class__):
            return False
        return self.host == other.host and self.port == other.port
def get_gateway_listen(gateway_listen: str) -> List[HostAndPort]:
    result = []
    for bind_address in gateway_listen.split(","):
        result.append(HostAndPort.parse(bind_address))
    return result
(
    
    LOCALSTACK_HOST,
    
    
    
    GATEWAY_LISTEN,
    
    EDGE_BIND_HOST,
    EDGE_PORT,
    EDGE_PORT_HTTP,
) = populate_legacy_edge_configuration(os.environ)
EDGE_FORWARD_URL = os.environ.get("EDGE_FORWARD_URL", "").strip()
DOCKER_BRIDGE_IP = os.environ.get("DOCKER_BRIDGE_IP", "").strip()
DOCKER_SDK_DEFAULT_TIMEOUT_SECONDS = int(os.environ.get("DOCKER_SDK_DEFAULT_TIMEOUT_SECONDS") or 60)
DOCKER_SDK_DEFAULT_RETRIES = int(os.environ.get("DOCKER_SDK_DEFAULT_RETRIES") or 0)
ENABLE_CONFIG_UPDATES = is_env_true("ENABLE_CONFIG_UPDATES")
DISABLE_CORS_HEADERS = is_env_true("DISABLE_CORS_HEADERS")
DISABLE_CORS_CHECKS = is_env_true("DISABLE_CORS_CHECKS")
DISABLE_CUSTOM_CORS_S3 = is_env_true("DISABLE_CUSTOM_CORS_S3")
DISABLE_CUSTOM_CORS_APIGATEWAY = is_env_true("DISABLE_CUSTOM_CORS_APIGATEWAY")
EXTRA_CORS_ALLOWED_HEADERS = os.environ.get("EXTRA_CORS_ALLOWED_HEADERS", "").strip()