### 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_
self,
        aws_client,
        s3_bucket,
        kms_create_key,
        snapshot,
    ):
        snapshot.add_transformer(
            [
                snapshot.transform.resource_name("SSEKMSKeyId"),
                snapshot.transform.key_value(
                    "Bucket", reference_replacement=False, value_replacement="<bucket>"
                ),
                snapshot.transform.key_value("Location"),
            ]
        )
        key_before_set = "test-sse-bucket-before"
        key_after_set = "test-sse-bucket-after"
        data = b"test-sse"
        key_id = kms_create_key()["KeyId"]
        response = aws_client.s3.put_(Bucket=s3_bucket, Key=key_before_set, Body=data)
        snapshot.match("put-obj-default-before-setting", response)
        response = aws_client.s3.get_(Bucket=s3_bucket, Key=key_before_set)
        snapshot.match("get-obj-default-before-setting", response)
        response = aws_client.s3.put_bucket_encryption(
            Bucket=s3_bucket,
            ServerSideEncryptionConfiguration={