refactor(NODE-3717): reorganize tests part 2

[dariakp]

Description

NODE-3717

What is changing?

• crud and bulk tests were moved to integration/crud; one prose test was separated into a prose file from bulk
• max staleness test were moved to integration/max-staleness - they use a mock server but I think it's better to make them into proper integration tests than convert to a unit test (see my comment on this PR and new ticket)
• load balancer, retryable reads, and retryable writes tests have all been moved into a corresponding integration directory

NOTE: The changes in this PR affect the configuration for run-serverless-tests.sh we should double check to make sure all desired tests are still running (see my comment on that file).

Is there new documentation needed for these changes?

N/A

What is the motivation for this change?

Better test organization

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>
• [N/A] Changes are covered by tests
• New TODOs have a related JIRA ticket

[durran]

I'm leaving the conversations unresolved so anyone else who wants a look can see them easily, but feel free to resolve them yourself when you want to merge. LGTM.