[Data] Added support for Joins (using hash-shuffle)

[alexeykudinkin]

Why are these changes needed?

This PR adds Dataset.join operator allowing 2 datasets to be joined using previously added Hash-shuffle implementation.

Currently following types of joins are supported:

• Inner (left/right)
• Outer (left/right)

In the future we'll be adding support for more join types.

Changes

• Added JoinOperator
• Added Dataset.join
• Added tests

Related issue number

Closes #18911 (Finally!!!)

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 :(

[richardliaw]

should this be part of SMD_API_GROUP, which would include zip/merge?

[alexeykudinkin]

Yeah, i can add to that group but i don't really understand the intention behind this grouping as it seems practically arbitrary in many cases

[richardliaw]

I believe the grouping names gets rendered for documentation for better user discovery (grouping APIs into subsections).

[richardliaw]

nice!!