there's no types for pipeline stages which i think could be a good addition. mongoose already has it. [mongoose pipeline stage](https://github.com/Automattic/mongoose/blob/0aa998371e2a6deffdf525770f81d5441f73f4cb/types/pipelinestage.d.ts#L5) the need for using as const for projection to allow exclusion can be eliminated with using const type parameter. I'm open to creating pull requests for both of these