DRIVERS-2865: Require drivers to always send out bypassDocumentValidation

[alcaeus]

Please complete the following before merging:

• Update changelog.
• Test changes in at least one language driver.
• Test these changes against all server versions and topologies (including standalone, replica set, sharded
  clusters, and serverless).

This effectively reverts #266 and adds tests for the behaviour. I've also decided to remove the rationale for sending bypassDocumentValidation: true in the bulk write specification as this difference no longer exists.

The new tests are grouped in a single file to make it easier for drivers to skip this particular test until they've had a chance to make the changes. No other test (aside client bulkWrite which already implements the new behaviour) use bypassDocumentValidation: false, so this change should not have any side effects in drivers.

[jmikola]

Test changes LGTM but I can't verify "Test changes in at least one language driver." Add a link to the related PR if possible.

[alcaeus]

Test changes LGTM but I can't verify "Test changes in at least one language driver." Add a link to the related PR if possible.

I tested this locally, but since we rely on libmongoc's bulk write implementation for all inserts, I was only testing the negative case. I was able to confirm that aggregate with $out works as expected.