Add examine_contents microservice

This new microservice runs a tool which attempts to extract meaningful
patterns and features from files. The primary tool run right now is
bulk_extractor, which is run on disk images and other files alike.

Refs #5880.
Examine contents: add admin option to control

Refs #5880.
preconfiguredChoices: Set based on UUID, not description

preconfiguredChoices were previously being matched via description
strings, which was error-prone. This replaces matching with precise
UUID matches instead.
Add internal comment to defaultProcessingMCP.xml