feat: support left join

sbroad-cartridge/test_app/test/data/config.yml

...tridge/test_app/test/integration/left_outer_join_test.lua

sbroad-core/src/backend/sql/ir.rs

sbroad-core/src/backend/sql/tree.rs

sbroad-core/src/errors.rs

sbroad-core/src/executor/bucket.rs

sbroad-core/src/executor/ir.rs

sbroad-core/src/frontend/sql.rs

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

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

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

sbroad-core/src/frontend/sql/ir/tests/single.rs

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

sbroad-core/src/ir/api/parameter.rs

sbroad-core/src/ir/distribution.rs

sbroad-core/src/ir/explain.rs

sbroad-core/src/ir/helpers.rs

sbroad-core/src/ir/operator.rs

sbroad-core/src/ir/operator/tests.rs

sbroad-core/src/ir/transformation.rs