Support for Apollo 4

[Hhovland]

I was investigating what dependencies in my project were needed to update to Apollo-server 4, and as of writing this is the only dependency that needs to be updated as type-graphql 2.0.0 now has a beta release that appears to be stable enough to function with Apollo-server 4, and you already have changes to support TypeORM 0.3.*. I mostly wanted to open this issue to do my due diligence since no other issues mention it.

At the very least if someone else has a solution to Apollo server 4 Plugin creation steps but I am not sure if any breaking changes were made in the beta type-graphql update that would cause type-graphql-dataloader to fail.