Unnecessary embeddable-related collections when ensureIndexes flag set to true

[cherfia]

Describe the bug
MikroORM creates unnecessary embeddable-related collections when it gets initialized with ensureIndexes set to true.

To Reproduce
Steps to reproduce the behavior in Nestjs framework:

1. Create an embeddable class

@Embeddable()
export class Address {
  
  @Property()
  street!: string;

  @Property()
  postalCode!: string;

  @Property()
  city!: string;

  @Property()
  country!: string;

}

2. Create an entity class which uses the above embeddable class to define one of its properties

@Entity({ collection: 'users' })
export class User {

  @Embedded()
  address!: Address;

}

3. Setup MikroORM configuration and enable ensureIndexes option

MikroOrmModule.forRootAsync({
      imports: [ConfigModule],
      inject: [ConfigService],
      useFactory: async (configService: ConfigService) => ({
        type: 'mongo',
        ensureIndexes: true,
        entities: [Address, User],
      }),
    }),

Running NestJS with such a configuration will result in generating two collections: users and address

Expected behavior
MikroORM should filter out embeddable classes from the entities array when it gets initialized. In other words, in our example, MikroORM should create only one single collection (i.e. users).

Versions

Dependency	Version
node	14.8.0
typescript	3.7.4
mikro-orm	4.2.3
@mikro-orm/mongodb	4.2.3