SERVER-44721: Change in AWS KMS response object breaks shell field level encryption

Description

A change in the expected response from AWS KMS broke the 4.2.0/4.2.1 mongo shell. A fix is upcoming, but we need an admonition until then.

 Once 4.2.2 releases, move admonition down to bottom of the section and advise users to update to 4.2.2 immediately. May also help to associate 4.2.2 as the 'GA" release of FLE.

This does not affect any of the official 4.2-compatible drivers, nor does it affect locally managed keys.