[Serve] Alias ray.serve.dag.InputNode

[simon-mo]

Why are these changes needed?

Because we can't expect users to type from ray.experimental.dag.input_node import InputNode when Serve deployment graph hits Beta/GA

Related issue number

Checks

• 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 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 :(

[edoakes]

@simon-mo should we put this under ray.serve.dag instead? Might be better to not pollute the top-level namespace. Your call.

[simon-mo]

yeah that's a good idea... from ray.serve import stuff smells a bit weird as well

[simon-mo]

changed

[edoakes]

@simon-mo should this and dagdriver come from the same import also? Depends on if we expect to have more builtin drivers in the future.

[simon-mo]

I'm still conflicted about the driver. On the one hand the drivers package is great and signify users can just add more and more drivers. on the other hand it's surely better to have one less import line...