fix(NODE-6241): allow Binary as local KMS provider key

[addaleax]

This aligns the types with actual behavior as well as the shell's expected set of supported types.

Description

What is changing?

Is there new documentation needed for these changes?

What is the motivation for this change?

Accurate TS

Release Highlight

The LocalKMSProviderConfiguration's key property accepts Binary

A local KMS provider at runtime accepted a BSON Binary instance but the Typescript inaccurately only permitted Buffer and string.

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