### 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_
snapshot.add_transformer(
            [
                snapshot.transform.key_value("BucketName"),
                snapshot.transform.key_value(
                    "Expiration", reference_replacement=False, value_replacement="<expiration>"
                ),
            ]
        )
        rule_id_1 = "rule_one"
        rule_id_2 = "rule_two"
        current_exp_days = 7
        lfc = {
            "Rules": [
                {
                    "ID": rule_id_1,
                    "Filter": {
                        "Tag": {
                            "Key": "testlifecycle",
                            "Value": "positive",
                        },
                    },
                    "Status": "Enabled",
                    "Expiration": {"Days": current_exp_days},
                },
                {