Add a setting/flag to report on documents

[daveaglick]

For example, "show me all documents that end up with a publish date in the future". One approach could be a module or pipeline that checks for this flag and then logs the report to the console. It would be nice to make it general, could use computed values evaluated against each document - I.e. --report "=> Published > DateTime.Today". Could also treat the value as metadata to check for true if just a string: --report Draft would check if GetBool("Draft") == true.

Need to consider if we should just check content pipeline outputs or data and other pipelines too, or if there should be a way to specify (--report-pipeline Data).

[daveaglick]

cc @patriksvensson