fix(NODE-5609): node driver omits base64 padding in sasl-continue command

[alenakhineika]

Description

Ensure that we don't strip padded "=" from saslStart responses that are passed to saslContinue.

What is changing?

We replace the existing parsing using split that kills trailing “=”s with regex parsing that preserves trailing “=”s.

Is there new documentation needed for these changes?

None

What is the motivation for this change?

NODE-5609

Release Highlight

The base64 padding is now preserved in the saslContinue command

The authentication was rejected by the saslContinue command from mongosh due to missing "=" padding from the client. We fixed the way we parse payload to preserve trailing "="s.

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

[W-A-James]

Failing tests are either known flaky or unrelated