fix: ensure buildBulkWriteOperations target shard if shardKey is set

[matlpriceshape]

Fixes #14622

Summary

When having a sharded collection and having set shardKey on the schema, using buildBulkWriteOperations does not take the shardKey into account.

The documention for shardKey states (https://mongoosejs.com/docs/guide.html#shardKey):

Each sharded collection is given a shard key which must be present in all insert/update operations

This PR enabled support for the shardKey option when using the buildBulkWriteOperations method.

Examples

Given this schema

const measurementSchema = new Schema({
  temperature: { type: Number },
  sensorId: { type: String },
}, { shardKey: { sensorId: 1 } });

const Measurement = db.model('Measurement',measurementSchema )

and assuming an saved document m, this bulkSave action will correctly include sensorId in the bulkWrite command:

m.temperature = 21.1

await Measurement.bulkWrite([m])
/* This will generate 

bulkWrite([
  {
    updateOne: {
      filter: {
        _id: ...,
        sensorId: 1
      },
      {
        update: {
          $set: {
            temperature: 21.1
          }
        }
      }
    },
  },
])

*/

[vkarpov15]

Thanks 👍