TypedDocumentNode for graphql-files-modules

I've written* a plugin that fills the same role as the `typescript-graphql-files-modules` plugin (importing .graphql files into typescript with graphql-loader or similar) but which types the exported operations with `TypedDocumentNode`s that integrate with the `typescript` plugin. There isn't, as far as I know, anything else in the `@graphql-codegen` ecosystem that integrates `TypedDocumentNode` with standalone graphql files like this.

- It wouldn't take much work to add a PR integrating the plugin into this repo or the main codegen repo. Config documentation and tests are already written.
- Alternatively, I could change the plugin's API a bit so it's backwards compatible with `typescript-graphql-files-modules` and then use it to replace that plugin entirely.

Would you be interested in a PR along these lines?

*Or really, forked from an [existing but out-of-date plugin](https://github.com/rubengrill/apollo-typed-documents).

---

So where the existing plugin generates this:

```typescript
declare module "*/UserOperations.gql" {
import { DocumentNode } from "graphql"
const defaultDocument: DocumentNode
export const NotificationPreference: DocumentNode
export const ExternalAccountStatus: DocumentNode
export const UserExternalAccountsStatus: DocumentNode
export const User: DocumentNode
export const UserProjects: DocumentNode
export const UserGet: DocumentNode
export const UsersList: DocumentNode
export const UsersCollection: DocumentNode
export const UserGetUserProjects: DocumentNode
export const UserSave: DocumentNode
export const UserSendInvitation: DocumentNode

export default defaultDocument
}
```
Mine generates this:
```typescript
declare module "*/UserOperations.gql" {
import { TypedDocumentNode } from "@graphql-typed-document-node/core";
import { UserGetQuery, UserGetQueryVariables } from "graphql/schema";
export const UserGet: TypedDocumentNode;
import { UsersListQuery, UsersListQueryVariables } from "graphql/schema";
export const UsersList: TypedDocumentNode;
import { UsersCollectionQuery, UsersCollectionQueryVariables } from "graphql/schema";
export const UsersCollection: TypedDocumentNode;
import { UserGetUserProjectsQuery, UserGetUserProjectsQueryVariables } from "graphql/schema";
export const UserGetUserProjects: TypedDocumentNode;
import { UserSaveMutation, UserSaveMutationVariables } from "graphql/schema";
export const UserSave: TypedDocumentNode;
import { UserSendInvitationMutation, UserSendInvitationMutationVariables } from "graphql/schema";
export const UserSendInvitation: TypedDocumentNode;
}
```

The location of the schema definitions, the location of TypedDocumentNode itself, and many other things are configurable.