### 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_
_key = "test-key-tagging"
        aws_client.s3.put_(Bucket=s3_bucket, Key=_key, Body="something")
        # get 
        s3_obj = aws_client.s3.get_(Bucket=s3_bucket, Key=_key)
        snapshot.match("get-obj", s3_obj)
        # dele
        aws_client.s3.delete__tagging(Bucket=s3_bucket, Key=_key)
        # asse
        s3_obj = aws_client.s3.get_(Bucket=s3_bucket, Key=_key)
        snapshot.match("get-obj-after-tag-deletion", s3_obj)
    @markers.aws.validated
    def test_delete_non_existing_keys_quiet(self, s3_bucket, snapshot, aws_client):
        _key = "test-key-nonexistent"
        aws_client.s3.put_(Bucket=s3_bucket, Key=_key, Body="something")
        response = aws_client.s3.delete_s(
            Bucket=s3_bucket,
            Delete={
                "s": [{"Key": _key}, {"Key": "dummy1"}, {"Key": "dummy2"}],
                "Quiet": True,
            },
        )
        snapshot.match("deleted-resp", response)
        assert "Deleted" not in response
        assert "Errors" not in response
    @markers.aws.validated
    def test_delete_non_existing_keys(self, s3_bucket, snapshot, aws_client):