### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When attempting to sign some document using Localstack KMS inside a lambda container (also running on localstack), the localstack KMS listener returns some unknown error.

The KMS key and lambda containers have been created from the same CDK app deploy, and I can see all the resources in the localstack web console.

The test application I'm using to prove this behaviour is available here:
https://github.com/LukaHedt/localstack_kms_test

Instructions to run are in the main Readme, and the `/localstack/Readme.md` file.

`aws-sdk` returns an unknown error, and the localstack docker logs that I receive are available here:
https://pastebin.com/58Z3fXi3

Have done an amount of testing and can confidently claim the following:
- Have tested on multiple machines with the same outcome
- Doesn’t make a difference if I specify an ARN or a KeyID in the signing request
- Downgrading localstack versions either didn’t make a difference, or I couldn’t actually deploy a localstack container with version 0.12.20 or lower.

### Expected Behavior

KMS Sign should return a signature for the given payload.

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

Test application demonstrating the current behaviour is available here:

https://github.com/LukaHedt/localstack_kms_test

Full instructions to run are in the `/localstack/Readme.md` file.


### Environment

```markdown
- OS: MacOS Monteray 12.3
- LocalStack: 0.14.0
```


### Anything else?

_No response_
CONFIG_DIR = os.environ.get("CONFIG_DIR", os.path.expanduser("~/.localstack"))
try:
    load_environment(CONFIG_PROFILE)
except ImportError:
    
    pass
if "DEFAULT_REGION" not in os.environ:
    os.environ["DEFAULT_REGION"] = os.environ.get("AWS_DEFAULT_REGION") or AWS_REGION_US_EAST_1
DEFAULT_REGION = os.environ["DEFAULT_REGION"]
HOSTNAME_EXTERNAL = os.environ.get("HOSTNAME_EXTERNAL", "").strip() or LOCALHOST
LOCALSTACK_HOSTNAME = os.environ.get("LOCALSTACK_HOSTNAME", "").strip() or LOCALHOST
DATA_DIR = os.environ.get("DATA_DIR", "").strip()
TMP_FOLDER = os.path.join(tempfile.gettempdir(), "localstack")
if TMP_FOLDER.startswith("/var/folders/") and os.path.exists("/private%s" % TMP_FOLDER):
    TMP_FOLDER = "/private%s" % TMP_FOLDER
HOST_TMP_FOLDER = os.environ.get("HOST_TMP_FOLDER", TMP_FOLDER)
CACHE_DIR = os.environ.get("CACHE_DIR", os.path.join(TMP_FOLDER, "cache")).strip()
VAR_LIBS_DIR = os.environ.get("VAR_LIBS_DIR", os.path.join(TMP_FOLDER, "var_libs")).strip()
LS_LOG = eval_log_type("LS_LOG")
DEBUG = is_env_true("DEBUG") or LS_LOG in TRACE_LOG_LEVELS
DEVELOP = is_env_true("DEVELOP")
DEVELOP_PORT = int(os.environ.get("DEVELOP_PORT", "").strip() or DEFAULT_DEVELOP_PORT)
WAIT_FOR_DEBUGGER = is_env_true("WAIT_FOR_DEBUGGER")
USE_SSL = is_env_true("USE_SSL")
USE_SINGLE_REGION = is_env_true("USE_SINGLE_REGION")
TF_COMPAT_MODE = is_env_true("TF_COMPAT_MODE")
DEFAULT_ENCODING = "utf-8"
DOCKER_SOCK = os.environ.get("DOCKER_SOCK", "").strip() or "/var/run/docker.sock"
DOCKER_FLAGS = os.environ.get("DOCKER_FLAGS", "").strip()
DOCKER_CMD = os.environ.get("DOCKER_CMD", "").strip() or "docker"