FIX-#6647: Added init file to make modin/experimental/sql/hdk/query.py part of modin package

[Egor-Krivov]

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What do these changes do?

This file is currently not part of modin package (for example, here in source files . To fix that we add __init__.py file to turn folder into normal python module.

• first commit message and PR title follow format outlined here

  NOTE: If you edit the PR title to match this format, you need to add another commit (even if it's empty) or amend your last commit for the CI job that checks the PR title to pick up the new PR title.

• passes flake8 modin/ asv_bench/benchmarks scripts/doc_checker.py
• passes black --check modin/ asv_bench/benchmarks scripts/doc_checker.py
• signed commit with git commit -s
• Resolves BUG: modin.experimental.sql.hdk.query is not part of modin package #6647
• tests added and passing
• module layout described at docs/development/architecture.rst is up-to-date

[dchigarev]

Thanks for the fix!

Although, each file (even an empty one) requires the license thing and sometimes a brief one-line docstring, otherwise CI won't pass I believe

Example:
https://github.com/modin-project/modin/blob/master/modin/core/dataframe/__init__.py

[Egor-Krivov]

Changed title to fit modin requirements and created issue