monolog: MWLoggerMonologSamplingHandler

Introduce the MWLoggerMonologSamplingHandler which can
be used to probabilistically sample the log event stream.

Bug: T85067
Change-Id: Icd14fc8c44ca9eef0f3f5cc4f1d1d8b68d517f07
Merge "monolog: MWLoggerMonologSamplingHandler"