[While hacking](https://trac.torproject.org/projects/tor/ticket/9380) 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: legacy/trac#12254