Add session name to api/version to easily identify cluster session

[alanwguo]

Why are these changes needed?

Let's callers easily identify which "session" of the cluster is currently running.

Related issue number

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• [x] 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
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  • [ ] Release tests
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