### 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_
"""
        Returns Localstack directory paths as they are defined within the container. Everything shared and writable
        lives in /var/lib/localstack or /tmp/localstack.
        :returns: Directories object
        """
        defaults = Directories.defaults()
        return Directories(
            static_libs=defaults.static_libs,
            var_libs=defaults.var_libs,
            cache=defaults.cache,
            tmp=defaults.tmp,
            functions=defaults.functions,
            data=defaults.data if PERSISTENCE else os.path.join(defaults.tmp, "state"),
            config=defaults.config,
            logs=defaults.logs,
            init=defaults.init,
        )
    @staticmethod
    def for_host() -> "Directories":