feat(NODE-5319): mark search index api public

[baileympearson]

Description

What is changing?

The search index API is marked public.

Also, @lerouxb noticed that the definition for SearchIndexModel was incorrect, although the code path (and our unified tests) do assert on the correct value at runtime. This PR fixes the type.

Is there new documentation needed for these changes?

Yes, docsp ticket.

What is the motivation for this change?

Release Highlight

Programmatic management of search indexes

This PR adds support for managing search indexes (creating, updating, deleting and listing indexes). The new methods are available on the Collection class.

const indexes = await collection.listSearchIndexes().toArray(); // produces an array of search indexes
await collection.createSearchIndex({ name: 'my-index', definition: < index definition > } ); 
await collection.updateSearchIndex('my-index', < new definition >);
await collection.dropSearchIndex('my-index');

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]

Was the test changes commit intended to be part of this? Could we just limit it to the API changes and move that commit to a new branch for the next steps?

[baileympearson]

@durran That was unintentional - somehow I had an extra commit from my search indexes work on main. I've rebased it away now