feat(NODE-5940): cache the AWS credentials provider in the MONGODB-AWS auth logic

[alenakhineika]

Description

Instead of creating a new AWS provider for each authentication, we cache the AWS credentials provider per client.

What is changing?

Backporting NODE-5616 to 5.x.

Is there new documentation needed for these changes?

None

What is the motivation for this change?

NODE-5940

Release Highlight

Caching AWS credentials provider per client

Instead of creating a new AWS provider for each authentication, we cache the AWS credentials provider per client to prevent overwhelming the auth endpoint and ensure that cached credentials are not shared with other clients.

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

[nbbeeken]

Seems like a straightforward backport, small test fix