### 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_
encrypted_key_material: CiphertextType,
        valid_to: DateType = None,
        expiration_model: ExpirationModelType = None,
    ) -> ImportKeyMaterialResponse:
        store = self._get_store(context)
        import_token = to_str(import_token)
        import_state = store.imports.get(import_token)
        if not import_state:
            raise NotFoundException(f"Unable to find key import token '{import_token}'")
        key_to_import_material_to = store.get_key(
            key_id, enabled_key_allowed=True, disabled_key_allowed=True
        )
        self._validate_key_for_encryption_decryption(key_to_import_material_to)
        if import_state.wrapping_algo == AlgorithmSpec.RSAES_PKCS1_V1_5:
            decrypt_padding = padding.PKCS1v15()
        elif import_state.wrapping_algo == AlgorithmSpec.RSAES_OAEP_SHA_1:
            decrypt_padding = padding.OAEP(padding.MGF1(hashes.SHA1()), hashes.SHA1(), None)
        elif import_state.wrapping_algo == AlgorithmSpec.RSAES_OAEP_SHA_256:
            decrypt_padding = padding.OAEP(padding.MGF1(hashes.SHA256()), hashes.SHA256(), None)
        else:
            raise KMSInvalidStateException(
                f"Unsupported padding, requested wrapping algorithm:'{import_state.wrapping_algo}'"
            )
        key_material = import_state.key.crypto_key.key.decrypt(
            encrypted_key_material, decrypt_padding
        )
        key_to_import_material_to.crypto_key.key_material = key_material
        return ImportKeyMaterialResponse()
    @handler("CreateAlias", expand=False)
    def create_alias(self, context: RequestContext, request: CreateAliasRequest) -> None: