Add new sql module

[dai-chen]

Issue #, if available: #264, #256

Description of changes: Add new SQL module to integrate with new query engine. As our start point, SELECT literal support is added.

Here are the major changes:

1. Add a new sql Gradle module.
2. Support SELECT literal by:
   2.1 Relaxing existing Project operator to accept Expression instead of ReferenceExpression.
   2.2 Adding a new Values operator for literal values which is correspondent with ANSI VALUES clause. Reference: https://modern-sql.com/feature/values, https://crate.io/docs/crate/reference/en/latest/sql/statements/values.html.
3. Integrate with legacy REST handler to route request to new SQL frontend.

The legacy module with all old code will co-exist with new sql module during code migration.

At runtime, request will send to new SQL parser first and fall back to old code if not supported yet.

Documentation: https://github.com/dai-chen/sql/blob/add-new-sql-module/docs/user/dql/expressions.rst

Testing: Passed old and new UT, IT and doctest.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[penghuo]

LGTM.

[chloe-zh]

LGTM, thanks!