add guide for gang scheduling with RayJob and Kueue

[andrewsykim]

Why are these changes needed?

Per discussion in https://github.com/ray-project/kuberay/issues/1890, we would like to add a guide on how to use RayJob and Kueue for gang scheduling.

Related issue number

https://github.com/ray-project/kuberay/issues/1890

Checks

• [X] 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 :(

[andrewsykim]

@kevin85421 this is ready for an initial review

[andrewsykim]

@angelinalg can you help review this PR please? It is similar to https://github.com/ray-project/ray/pull/42903

[kevin85421]

The following process will be similar to https://github.com/ray-project/ray/pull/42903#issuecomment-1925205038.

[kevin85421]

I have already requested Ray doc team to review this PR.

[andrewsykim]

Thanks for the review @angelinalg, addressed your comments!