feat: support arbitrary expr as a part of projection

.../test_app/test/integration/arbitrary_expressions_test.lua

sbroad-cartridge/test_app/test/integration/explain_test.lua

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

sbroad-core/src/frontend/sql.rs

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

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

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

sbroad-core/src/ir/explain.rs

sbroad-core/src/ir/expression.rs

...tifactory/backend/sql/tree/arbitrary_projection_plan.yaml

...ts/artifactory/frontend/sql/arbitrary_projection_ast.yaml

...s/artifactory/frontend/sql/arithmetic_projection_ast.yaml