### 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_
Bucket=bucket_2, Key=key_name, Body=data, ServerSideEncryption="aws:kms"
        )
        snapshot.match("put-obj-default-kms-s3-key-bucket-2", response)
        response = aws_client.s3.get_(Bucket=bucket_2, Key=key_name)
        snapshot.match("get-obj-default-kms-s3-key-bucket-2", response)
        response = aws_client.s3.put_bucket_encryption(
            Bucket=bucket_1,
            ServerSideEncryptionConfiguration={
                "Rules": [
                    {
                        "ApplyServerSideEncryptionByDefault": {
                            "SSEAlgorithm": "aws:kms",
                        },
                        "BucketKeyEnabled": True,
                    }
                ]
            },
        )
        snapshot.match("put-bucket-encryption-default-kms-s3-key", response)
        response = aws_client.s3.get_bucket_encryption(Bucket=bucket_1)
        snapshot.match("get-bucket-encryption-default-kms-s3-key", response)
        key_name = "test-sse-default-key-from-bucket"
        response = aws_client.s3.put_(
            Bucket=bucket_1, Key=key_name, Body=data, ServerSideEncryption="aws:kms"
        )
        snapshot.match("put-obj-default-kms-s3-key-from-bucket", response)
        response = aws_client.s3.get_(Bucket=bucket_1, Key=key_name)
        snapshot.match("get-obj-default-kms-s3-key-from-bucket", response)
    @markers.aws.validated
    def test_s3_analytics_configurations(self, aws_client, s3_create_bucket, snapshot):