Generics on ogm

[danstarns]

Description

Simple addition allows the use of a generic when calling .model on the OGM. This enables users to define their own types for each method, for example:

const ogm = new OGM({ typeDefs, driver });

class MyCustomModel {
    constructor() {}

    async find(args: { where: { id: string } }): Promise<{ id: string; password: string }[]> {
        return [];
    }
}

const User = ogm.model<MyCustomModel>("User");

Then you'd get autocomplete like this:

Tech-savvy users could use a graphql code gen and have full autocomplete via using this method.

Issue

Related to #174

Checklist

The following requirements should have been met (depending on the changes in the branch):

• Documentation has been updated
• TCK tests have been updated
• Integration tests have been updated
• Example applications have been updated
• New files have copyright header
• CLA (https://neo4j.com/developer/cla/) has been signed