Ticket #24838 - Added ability to associate publishes and versions with a task

This adds a new setting that is a string which will be turned into a filter for a shotgun query.  A string is used since lists in the settings files can't have different value types, and I wanted to allow for the values in the filter to be either strings, entities, or ints.

This was needed to allow the published Nuke file to be a valid sgtk publish, since the context that is used can be a task context (specifying the Step param) but the publishes didn't have a valid task before this.