fix(NODE-6407): use conversationId returned from server in saslContinue

[W-A-James]

Description (copied from #4258)

MONGODB-AWS authentication mechanism should follow SASL spec. Current implementation ignores the conversationId sent by the server and uses a hardcoded integer for all saslContinue messages across all conversations.

What is changing?

• Changing the hardcoded integer for conversationId to utilize the one that gets returned in the saslStart response.
• Add integration test to verify that saslContinue uses the conversationId returned by saslStart

Is there new documentation needed for these changes?

No. This change brings the implementation to spec.

What is the motivation for this change?

This is a bug. MONGODB-AWS authentication failed on database emulating MongoDB.

Release Highlight

Fixes SASL implementation for MONGODB-AWS to use conversationId returned by the server instead of hardcoded integer.

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