Clarify who learns about ContactInfo.

Explicitly include bridges, and note that we archive and publish all
descriptors.

(We are not yet publishing ContactInfo lines contained in bridge
descriptors, but maybe we'll want to do that soon, so let's err on the
side of caution here.)

Related to #9854.
Changes file for 9854
Merge remote-tracking branch 'origin/maint-0.2.4'