Convert datanommer.consumer to use fedora-messaging

[ryanlerch]

Currently the datanommer consumer consumes messages from the fedmsg queue. We currently get all messages due to the bridges, but we need to convert the consumer to use fedora-messaging.

The likely approach here will be to convert the consumer code to a fedora-messaging callback (https://fedora-messaging.readthedocs.io/en/stable/consuming.html#the-callback)

and run the consumer with a command like:

fedora-messaging consume --callback=datanommer.consumer:Nommer