### 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_
paths=["$..ServerSideEncryption"],
    )
    @pytest.mark.parametrize("tagging_directive", ["COPY", "REPLACE", None])
    def test_s3_copy_tagging_directive(self, s3_bucket, snapshot, aws_client, tagging_directive):
        snapshot.add_transformer(snapshot.transform.s3_api())
        _key = "source-"
        resp = aws_client.s3.put_(
            Bucket=s3_bucket, Key=_key, Body="test", Tagging="key1=value1"
        )
        snapshot.match("put-", resp)
        get__tags = aws_client.s3.get__tagging(Bucket=s3_bucket, Key=_key)
        snapshot.match("get--tag", get__tags)
        kwargs = {"TaggingDirective": tagging_directive} if tagging_directive else {}
        _key_copy = f"{_key}-copy"
        resp = aws_client.s3.copy_(
            Bucket=s3_bucket,
            CopySource=f"{s3_bucket}/{_key}",
            Key=_key_copy,
            Tagging="key2=value2",
            **kwargs,
        )
        snapshot.match("copy-", resp)
        get__tags = aws_client.s3.get__tagging(Bucket=s3_bucket, Key=_key_copy)
        snapshot.match("get-copy--tag", get__tags)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_s3_copy_content_type_and_metadata(self, s3_create_bucket, snapshot, aws_client):