feat(sql): support UNION

Summary

• feat(sql): support UNION

• update sbroad submodule to commit with support of UNION operator
• add integration tests for global tables (sharded tables were tested in cartridge tests)
• Usage:

select a from t union select b from t2

• Close sbroad#610 (closed)
• Changes should be cherry-picked to 24.2: no
• Docs follow-up: docs#249 (closed)
• Depends on sbroad!423 (merged)