Add support to generate an event per log file

[jspaleta]

Feature request from customer needs design discussion.

Desired use case explanation

Plugin now supports processing multiple files using a filename regexp pattern, and a state directory to hold per file path information, and will generate a single event capturing the result information.

The request is to generate an unique event for each processed log file path.

The technical problem

each generated event needs to have an unique check name, but file paths as check names might not be suitable, as file paths can be arbitrarily long and have special characters that can not be used in the check names currently.

Any attempt to squash the file path into an uuid makes the check name potentially unreadable to a human who needs to parse the event. Any attempt to shorten the filepath into a reasonable length check name runs the risk of destroying check name uniqueness causes events to overwrite each other.