This change adds a new server parameter to control the number of samples to draw from each user collection that has change stream pre-images enabled.
The number of samples was previously hard-coded to 10, and is now configurable at server startup and at runtime by setting the new `changeStreamPreImagesSamplePointsPerUUID` server parameter. The parameter can be used as a runtime mitigation in case pre-image sampling is found to consume too many I/O resources.

The server parameter default value is still 10, and the minimum value is 1.