### 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_
@markers.aws.validated
    @pytest.mark.parametrize(
        "storage_class",
        [
            StorageClass.STANDARD,
            StorageClass.STANDARD_IA,
            StorageClass.GLACIER,
            StorageClass.GLACIER_IR,
            StorageClass.REDUCED_REDUNDANCY,
            StorageClass.ONEZONE_IA,
            StorageClass.INTELLIGENT_TIERING,
            StorageClass.DEEP_ARCHIVE,
        ],
    )
    def test_put__storage_class(self, s3_bucket, snapshot, storage_class, aws_client):
        key_name = "test-put--storage-class"
        aws_client.s3.put_(
            Bucket=s3_bucket,
            Key=key_name,
            Body=b"body-test",
            StorageClass=storage_class,
        )
        response = aws_client.s3.get__attributes(
            Bucket=s3_bucket,
            Key=key_name,
            Attributes=["StorageClass"],
        )
        snapshot.match("get--storage-class", response)
    @markers.aws.validated
    def test_put__storage_class_outposts(