Add upcoming flink-runtime to the autolabeler config

[kbendick]

There's an open PR from @openinx to add a flink-runtime module. We should be labeling this new top level directory under the flink label, just like we bundle all of the various top level spark directories under one spark tag.

Here's the PR in question that adds the flink-runtime directory: #1423

[kbendick]

Closing this issue as the PR has been merged. I believe once another push happens against #1423 that the autolabeler might run again, though it's possible it only runs on PR creation.