### 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_
"""Return directories used for running localstack in host mode. Note that these are *not* the directories
        that are mounted into the container when the user starts localstack."""
        root = os.environ.get("FILESYSTEM_ROOT") or os.path.join(
            LOCALSTACK_ROOT_FOLDER, ".filesystem"
        )
        root = os.path.abspath(root)
        defaults = Directories.for_container()
        tmp = os.path.join(root, defaults.tmp.lstrip("/"))
        data = os.path.join(root, defaults.data.lstrip("/"))
        return Directories(
            static_libs=os.path.join(root, defaults.static_libs.lstrip("/")),
            var_libs=os.path.join(root, defaults.var_libs.lstrip("/")),
            cache=os.path.join(root, defaults.cache.lstrip("/")),
            tmp=tmp,
            functions=os.path.join(root, defaults.functions.lstrip("/")),
            data=data if PERSISTENCE else os.path.join(tmp, "state"),
            config=os.path.join(root, defaults.config.lstrip("/")),
            init=os.path.join(root, defaults.init.lstrip("/")),
            logs=os.path.join(root, defaults.logs.lstrip("/")),
        )
    @staticmethod
    def for_cli() -> "Directories":