Provide information about the file events were sourced from in schedule:list

[tip2tail]

Description
I want to know which file a particular scheduled event is defined in. This information is not currently exposed in either the table or JSON output format.

In my use-case I want to have this information in the JSON format so it can be machine-parsed.

Example
The table and JSON output of schedule:list should show the filename of the event/schedule.

Note It is my intention to submit a PR for this feature.