feat: add projecting and primary keys for virtual tables

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

sbroad-core/src/executor/engine/helpers.rs

sbroad-core/src/executor/engine/helpers/vshard.rs

sbroad-core/src/executor/ir.rs

sbroad-core/src/executor/vtable.rs

sbroad-core/src/executor/vtable/tests.rs

sbroad-core/src/ir/operator.rs

sbroad-core/src/ir/relation.rs

sbroad-core/src/ir/transformation/redistribution.rs

sbroad-core/src/ir/transformation/redistribution/groupby.rs