[Core] Add bundle_label_selector scheduling logic

[ryanaoleary]

Why are these changes needed?

This PR adds the bundle_label_selector option to Ray PlacementGroups, applying the label selectors on a per-bundle level to define label constraints for scheduling bundles on a node.

This PR passes the bundle_label_selector from the PlacementGroup options to the Raylet where the PlacementGroupSpec is built. Inside PlacementGroupSpec, each label selector is added to its corresponding Bundle message, and then added to the ResourceRequest in ComputeResources when the BundleSpec is constructed. This enables the cluster resource scheduler to check for required labels when calling IsFeasible and IsAvailable on a Node.

Related issue number

#51564

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 :(

[MengjinYan]

Thanks!

[MengjinYan]

@dayshah or @israbbani Do you mind take a brief look from c++'s perspective to see if there is any c++ particular comments? Thanks!

[dayshah]

one minor cpp nit, otherwise lgtm from cpp perspective. +1 on @MengjinYan comments