### 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_
# buck
        snapshot.add_transformer(snapshot.transform.s3_api())
        bucket_name = f"TESTUPPERCASE-{short_uid()}"
        with pytest.raises(ClientError) as e:
            s3_create_bucket(Bucket=bucket_name)
        snapshot.match("uppercase-bucket", e.value.response)
    @markers.aws.validated
    def test_create_bucket_with_existing_name(self, s3_create_bucket, snapshot, aws_client):
        snapshot.add_transformer(snapshot.transform.s3_api())
        bucket_name = f"bucket-{short_uid()}"
        s3_create_bucket(
            Bucket=bucket_name,
            CreateBucketConfiguration={"LocationConstraint": "us-west-1"},
        )
        for loc_constraint in ["us-west-1", "us-east-2"]:
            with pytest.raises(ClientError) as e:
                aws_client.s3.create_bucket(
                    Bucket=bucket_name,
                    CreateBucketConfiguration={"LocationConstraint": loc_constraint},
                )
            e.match("BucketAlreadyOwnedByYou")
            snapshot.match(f"create-bucket-{loc_constraint}", e.value.response)
    @markers.aws.validated
    @pytest.mark.skipif(
        reason="asf provider: routing for region-path s not working; "
        "both provider: return 200 for other regions (no redirects)"
    )
    def test_access_bucket_different_region(self, s3_create_bucket, s3_vhost_client, aws_client):