feat: support subqueries for global tables

Summarize the changes

• feat: support subqueries for global tables

• subqueries reading from global tables are supported
• subqueries in queries which scan the global tables are allowed: select a from global where b in (select c from segment)

However currently using global tables in join is not supported.

Ensure that

• New code is covered by unit and integration tests.
• Related issues would be automatically closed with gitlab's closing pattern (Closes #1, #2).
• Public modules are documented (check the rendered version with cargo doc --open).
• (if PEST grammar is changed) EBNF grammar reflects these changes (check the result with railroad diagram generator.

Next steps

• Update sbroad submodule in picodata/picodata.
• (if EBNF grammar is changed) create a follow-up issue in picodata/docs.

Closes #519 (closed)