### 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_
if key.metadata["KeyUsage"] != "ENCRYPT_DECRYPT":
            raise InvalidKeyUsageException(
                "KeyUsage for encryption / decryption should be ENCRYPT_DECRYPT"
            )
    def _validate_key_for_sign_verify(self, key: KmsKey):
        if key.metadata["KeyUsage"] != "SIGN_VERIFY":
            raise InvalidKeyUsageException(
                "KeyUsage for signing / verification key should be SIGN_VERIFY"
            )
    def _validate_grant_request(self, data: Dict, store: KmsStore):
        if "KeyId" not in data or "GranteePrincipal" not in data or "Operations" not in data:
            raise ValidationError("Grant ID, key ID and grantee principal must be specified")
        for operation in data["Operations"]:
            if operation not in VALID_OPERATIONS:
                raise ValidationError(
                    f"Value {['Operations']} at 'operations' failed to satisfy constraint: Member must satisfy"
                    f" constraint: [Member must satisfy enum value set: {VALID_OPERATIONS}]"
                )
def set_key_managed(key_id: str, account_id: str, region: str) -> None:
    store = kms_stores[account_id][region]
    key = store.get_key(key_id)
    key.metadata["KeyManager"] = "AWS"