Allow to specify connection for @InjectModel() decorator

I'm submitting a...

[ ] Regression
[ ] Bug report
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

Currently, you can't inject the same model for two different connections.

Expected behavior

Minimal reproduction of the problem with instructions

@Injectable()
export class FooService {
   constructor(
       @InjectModel(User.name) private userModel: Model<User>,
       @InjectModel(User.name) private readonlyUserModel: Model<User>
       ) {} 
}

@Module({
  imports: [MongooseModule.forFeatureAsync(..., DEFAULT_DB_CONNECTION), MongooseModule.forFeatureAsync(..., READONLY_DB_CONNECTION)]
  providers: [FooService]
})
export class FooModule {}

What is the motivation / use case for changing the behavior?

This is important for read scaling Mongo databases if you use multi-document transactions. Reads in transaction have to read from primary node, but other workloads can read from secondary nodes.

Therefore, workarounds are required for inject two models (eg. reexporting Model<User> from another module with custom provider token).

Another use case is security - limiting user privileges limits potential impact of query injection.

Environment

Newest versions of everything.

nestjs / mongoose

Allow to specify connection for @InjectModel() decorator #1014