feat(NODE-6419): deprecate explain options API for find and aggregate

[baileympearson]

Description

What is changing?

collection.find({}, { explain: ... }) and collection/db.aggregate({}, { explain: ... }) are deprecated.

Is there new documentation needed for these changes?

What is the motivation for this change?

Release Highlight

Find and Aggregate Explain in Options is Deprecated

Specifying explain for cursors in the operation's options is deprecated in favor of the .explain() methods on cursors:

collection.find({}, { explain: true })
// -> collection.find({}).explain()

collection.aggregate([], { explain: true })
// -> collection.aggregate([]).explain()

db.find([], { explain: true })
// -> db.find([]).explain()

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