### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
response = aws_client.s3.head_(Bucket=s3_bucket, Key=key)
        snapshot.match("head--expiry-current-without-version-id", response)
        # asse
        assert response["VersionId"] == version_id_2
        parsed_exp_date, parsed_exp_rule = parse_expiration_header(response["Expiration"])
        assert parsed_exp_rule == rule_id
        # use 
        assert (
            current_exp_days - 1
            <= (parsed_exp_date - response["LastModified"]).days
            <= current_exp_days + 1
        )
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test__expiry_after_bucket_lifecycle_configuration(
        self, s3_bucket, snapshot, aws_client
    ):
        snapshot.add_transformer(
            [
                snapshot.transform.key_value("BucketName"),
                snapshot.transform.key_value(
                    "Expiration", reference_replacement=False, value_replacement="<expiration>"
                ),
            ]
        )
        key = "test--expiry"
        put_ = aws_client.s3.put_(Body=b"test", Bucket=s3_bucket, Key=key)