### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

Currently, we always [calculate](https://github.com/localstack/localstack/blob/256b0de1f1a6085d3994e8d1322c763962ded2f0/localstack/services/kms/models.py#L229-L230) SHA256 digests for messages with `RAW` [MessageType](https://docs.aws.amazon.com/kms/latest/APIReference/API_Sign.html#API_Sign_RequestSyntax).

It is not clear if this is compatible with AWS. There are some reports like [this one](https://github.com/localstack/localstack/issues/6815#issuecomment-1309882776) about our implementation of Sign / Verify not working properly. Could be due to these digests.

What has to be done:
1. Should try to figure out how AWS calculates digests, whether the same algorithm is always used, or if digests are based on [SigningAlgorithm](https://docs.aws.amazon.com/kms/latest/APIReference/API_Sign.html#API_Sign_RequestSyntax). For this we can try importing the same key material into both AWS and LocalStack, use the resulting keys to sign the same message and then compare the signatures. If that works. If not - we can try just creating a key in AWS, sign a message with AWS, export the public key and then go through different digest algorithms in LocalStack, trying to verify the signed message with the obtained public key.
2. If the issue is really in our implementation of digests - should fix the digest logic.

### 🧑‍💻 Implementation

_No response_

### Anything else?

_No response_
elif ":key/" in some_id:
                key_arn = some_id
                key_id = key_arn.split(":key/")[1]
                parsed_arn = parse_arn(key_arn)
                if parsed_arn["region"] != self._region_name:
                    raise NotFoundException(f"Invalid arn {parsed_arn['region']}")
            else:
                raise ValueError(
                    f"Supplied value of {some_id} is an ARN, but neither of a KMS key nor of a KMS key "
                    f"alias"
                )
        elif some_id.startswith("alias/"):
            alias_name = some_id
        else:
            key_id = some_id
        if alias_name:
            self._create_alias_if_reserved_and_not_exists(alias_name, account_id, region)
            if alias_name not in self.aliases:
                raise NotFoundException(f"Unable to find KMS alias with name {alias_name}")
            key_id = self.aliases[alias_name].metadata["TargetKeyId"]
        
        if not PATTERN_UUID.match(key_id) and not MULTI_REGION_PATTERN.match(key_id):
            raise NotFoundException(f"Invalid keyId {key_id}")
        if key_id not in self.keys:
            if not key_arn:
                key_arn = f"arn:aws:kms:{self._region_name}:{self._account_id}:key/{key_id}"
            raise NotFoundException(f"Key '{key_arn}' does not exist")
        return key_id
kms_stores = AccountRegionBundle("kms", KmsStore)