Make model operations wait on Model.init()?

[vkarpov15]

Re: #8786 , other issues.

Testing transactions, unique constraints, change streams, etc. is confusing because you need to call Model.init() under the hood to wait for indexes to build and for Mongoose to create the collection (if you set the autoCreate option). It would be great if we could make Mongoose automatically create collections for models and block startSession() and watch() until the collection is created.

Also see #8814