### 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_
EXTRA_CORS_EXPOSE_HEADERS = os.environ.get("EXTRA_CORS_EXPOSE_HEADERS", "").strip()
EXTRA_CORS_ALLOWED_ORIGINS = os.environ.get("EXTRA_CORS_ALLOWED_ORIGINS", "").strip()
DISABLE_PREFLIGHT_PROCESSING = is_env_true("DISABLE_PREFLIGHT_PROCESSING")
DISABLE_EVENTS = is_env_true("DISABLE_EVENTS")
DEBUG_ANALYTICS = is_env_true("DEBUG_ANALYTICS")
DEBUG_HANDLER_CHAIN = is_env_true("DEBUG_HANDLER_CHAIN")
EAGER_SERVICE_LOADING = is_env_true("EAGER_SERVICE_LOADING")
SKIP_INFRA_DOWNLOADS = os.environ.get("SKIP_INFRA_DOWNLOADS", "").strip()
SKIP_SSL_CERT_DOWNLOAD = is_env_true("SKIP_SSL_CERT_DOWNLOAD")
CUSTOM_SSL_CERT_PATH = os.environ.get("CUSTOM_SSL_CERT_PATH", "").strip()
ALLOW_NONSTANDARD_REGIONS = is_env_true("ALLOW_NONSTANDARD_REGIONS")
if ALLOW_NONSTANDARD_REGIONS:
    os.environ["MOTO_ALLOW_NONEXISTENT_REGION"] = "true"
MAIN_CONTAINER_NAME = os.environ.get("MAIN_CONTAINER_NAME", "").strip() or "localstack_main"
LOCALSTACK_BUILD_GIT_HASH = os.environ.get("LOCALSTACK_BUILD_GIT_HASH", "").strip() or None
LOCALSTACK_BUILD_DATE = os.environ.get("LOCALSTACK_BUILD_DATE", "").strip() or None
OUTBOUND_HTTP_PROXY = os.environ.get("OUTBOUND_HTTP_PROXY", "")
OUTBOUND_HTTPS_PROXY = os.environ.get("OUTBOUND_HTTPS_PROXY", "")
ARN_PARTITION_REWRITING = is_env_true("ARN_PARTITION_REWRITING")
FORCE_SHUTDOWN = is_env_not_false("FORCE_SHUTDOWN")
MOCK_UNIMPLEMENTED = is_env_true("MOCK_UNIMPLEMENTED")
no_proxy = ",".join([constants.LOCALHOST_HOSTNAME, LOCALHOST, LOCALHOST_IP, "[::1]"])
if os.environ.get("no_proxy"):
    os.environ["no_proxy"] += "," + no_proxy
elif os.environ.get("NO_PROXY"):
    os.environ["NO_PROXY"] += "," + no_proxy
else:
    os.environ["no_proxy"] = no_proxy
CLI_COMMANDS = {}
if not DOCKER_BRIDGE_IP: