BridgeAuth should add a `published` line to bridge networkstatus documents

While hacking on getting BridgeDB to use Stem's descriptor parsers, I noticed that @type bridge-network-status 1.0 documents do not have a published line, like other networkstatus documents. I proposed that a new @type bridge-network-status 1.1 descriptor type is created, where Bridge Authorities add a published line to the head of the document.

Related: #12254 (moved)