feat(NODE-7009): add client metadata on demand

[durran]

Description

Allows appending driver info for the client metadata after a mongo client has been constructed.

What is changing?

• Adds appendMetadata to MongoClient
• Adds the ability for certain metadata to be modified on the client instance.
• Allows for appending metadata multiple times for the handshake.
• Syncs unified tests allowing for new functionality.
• Updates prose handshake tests.

Is there new documentation needed for these changes?

Manual docs.

What is the motivation for this change?

NODE-7009

Release Highlight

Clients now can add handshake metadata post construction

Driver information such as name, version, and platform are allowed:

import { MongoClient } from 'mongodb';

const client = new MongoClient(process.env.MONGODB_URI);
client.appendMetadata({ name: 'my library', version: '1.0', platform: 'NodeJS' });

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[durran]

This put Claude in an infinite loop. We omit/pick some of our readonly client options in order to modify them while the rest remain immutable. This means they cannot be internal if we want to modify them in this fashion, and now the metadata on the client with this feature is no longer immutable.

[dariakp]

if additionalDriverInfo is always defaulted to [], what could cause it to become unset?

[durran]

Our test suite doesn't have the same strict type restrictions and can be directly unset there. I considered that out of scope and to defensively program here.