More fields for Master status output

Created by: dominikwerder

Added top-level type key.

Added a few counter. More to come in another PR.

Example:

{
  "type": "filewriter_status_master",
  "files": {
    "the_job_id": {
      "filename": "nexus-output.h5",
      "topics": {
        "kafka_topic_number_one": {
          "messages_processed": 632,
          "error_message_too_small": 0,
          "error_no_flatbuffer_reader": 0,
          "error_no_source_instance": 0
        }
      }
    }
  }
}