feat: add tool to generate OpenAPI spec

[wpf500]

This PR adds experimental generation of an OpenAPI spec

It uses the packages routing-controllers-openapi and class-validator-jsonchema to generate the OpenAPI spec. It needs quite a bit of nudging in the right direction with extra decorators due to limitations in TypeScript type reflection.

In particular:

• All route handlers which return a Promise<T> (so basically all of them) have a @ResponseSchema(T) decorator
• There is now a separate DTO for each paginated response, e.g. PaginatedDto<GetContactDto> -> GetContactListDto. This is because class-validation-schema can't process generics, so derived classes are necessary
• DTOs that were extended from another DTO but without new properties (e.g. GetAddressDto extends from UpdateAddressDto) have been merged. This was only an attempt at consistency and class-validation-schema can't generate JSONSchema for these classes (as they aren't registered with class-validator)

This means there is quite a lot of boilerplate in controllers and on DTOs, but I think it's good enough for now and pretty cool to be able to generate some fairly useable docs so easily :).

To do

• Backport some new DTOs (GetSignupFlowDto, etc.) to feat: validate API responses #333
• Fix the GET /content/:id endpoint

The docs 📖