feat(sql): mock DDL create schema, drop schema

...d/sbroad-cartridge/test_app/test/integration/ddl_test.lua

sbroad/sbroad-core/src/frontend/sql.rs

sbroad/sbroad-core/src/frontend/sql/query.pest

sbroad/sbroad-core/src/ir.rs

sbroad/sbroad-core/src/ir/node.rs

sbroad/sbroad-core/src/ir/node/ddl.rs

src/pgproto/backend/describe.rs

src/sql.rs

test/pgproto/extended_query_test.py

test/pgproto/simple_query_test.py