add id alias for json object to override default _id

[derekrliang]

This allows the returned JSON entity object to have a custom key such as id instead of the default MongoDB id _id.

Example:

const DbMixin = (collection: string) => {
  return {
    mixins: [DbService],
    adapter: new MongoAdapter(
      process.env.MONGO_URI, {
        useNewUrlParser: true,
        useUnifiedTopology: true,
        jsonId: "id",
      }
    ),
    collection,
  };
};

[coveralls]

Coverage decreased (-0.2%) to 93.536% when pulling 7796bfc on derekrliang:feature/add-id-alias-json-obj into c2f9d43 on moleculerjs:master.

[coveralls]

Coverage decreased (-0.2%) to 93.536% when pulling 0f416d3 on derekrliang:feature/add-id-alias-json-obj into c2f9d43 on moleculerjs:master.

[icebob]

Missing unit tests

[devalexandre]

could

constructor(uri, opts = { }, dbName)