### 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_
"ENABLE_CONFIG_UPDATES",
    "ES_CUSTOM_BACKEND",
    "ES_ENDPOINT_STRATEGY",
    "ES_MULTI_CLUSTER",
    "EXTRA_CORS_ALLOWED_HEADERS",
    "EXTRA_CORS_ALLOWED_ORIGINS",
    "EXTRA_CORS_EXPOSE_HEADERS",
    "HOSTNAME",
    "HOSTNAME_EXTERNAL",
    "HOSTNAME_FROM_LAMBDA",
    "KINESIS_ERROR_PROBABILITY",
    "KINESIS_INITIALIZE_STREAMS",
    "LAMBDA_CODE_EXTRACT_TIME",
    "LAMBDA_CONTAINER_REGISTRY",
    "LAMBDA_DOCKER_DNS",
    "LAMBDA_DOCKER_FLAGS",
    "LAMBDA_DOCKER_NETWORK",
    "LAMBDA_EXECUTOR",
    "LAMBDA_FALLBACK_URL",
    "LAMBDA_FORWARD_URL",
    "LAMBDA_JAVA_OPTS",
    "LAMBDA_REMOTE_DOCKER",
    "LAMBDA_REMOVE_CONTAINERS",
    "LAMBDA_STAY_OPEN_MODE",
    "LAMBDA_TRUNCATE_STDOUT",
    "LEGACY_DOCKER_CLIENT",
    "LOCALSTACK_API_KEY",
    "LOCALSTACK_HOSTNAME",
    "LOG_LICENSE_ISSUES",
    "LS_LOG",