Why are these changes needed?

1. Add --labels param in ray start command-line to setting node labels

ray start --head --labels='{"gpu_type": "A100", "region": "us"}'

2. Add a new field "Labels" to the ray.nodes() API to getting the labels of each node.

ray.nodes()[0]["Labels"] == {"gpu_type": "A100", "region": "us"}

3. Add a basic test case
   python/ray/tests/test_node_labels.py
   Other exceptional scenarios and boundary scenarios testing will be added later by new PR.

Related issue number

Enhancing node affinity scheduling feature through node labels #34894

(P1)Finalize the command-line API(ray start) for setting node labels.

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(