### 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("VersionId"))
        _key = "locked-"
        bucket_name = s3_create_bucket(LockEnabledForBucket=True)
        put_obj = aws_client.s3.put_(
            Bucket=bucket_name,
            Key=_key,
            Body="test",
            LockLegalHoldStatus="ON",
        )
        snapshot.match("put-obj", put_obj)
        version_id = put_obj["VersionId"]
        head_ = aws_client.s3.head_(Bucket=bucket_name, Key=_key)
        snapshot.match("head--with-legal-hold", head_)
        # disa
        put_legal_hold = aws_client.s3.put__legal_hold(
            Bucket=bucket_name,
            Key=_key,
            VersionId=version_id,
            LegalHold={"Status": "OFF"},
        )
        snapshot.match("put--legal-hold-off", put_legal_hold)
    @markers.aws.validated
    @pytest.mark.skipif(
        condition=LEGACY_V2_S3_PROVIDER,
        reason="Behaviour is not implemented, does not validate",
    )
    def test_put__legal_hold_exc(self, s3_create_bucket, snapshot, aws_client):