Provide option to overwrite pre-existing documents

[SkeloGH]

Is your feature request related to a problem? Please describe.
Pre-existing documents aren't updated if fresher info is available

Describe the solution you'd like
Provide a feature gate mechanism that allows to turn on or off updating documents.

Describe alternatives you've considered
Manually overriding documents that aren't copied

Additional context

This is the current implementation where it's decided to return the already saved document.

• src/clients/mongodb/index.js

saveDocument = (document) => {
    const collection = document.dataSet;
    const { _id } = document.data;
    const query = { _id };

    return this.db.collection(collection)
      .findOne(query)
      .then((result) => {
        if (result) return this.handleSavedDocument(result);
        return this.db.collection(collection).insertOne(document.data);
      });
  }