client/authority-discovery: Publish and query on exponential interval

When a node starts up publishing and querying might fail due to various
reasons, for example due to being not yet fully bootstrapped on the DHT.
Thus one should retry rather sooner than later. On the other hand, a
long running node is likely well connected and thus timely retries are
not needed. For this reasoning use an exponentially increasing interval
for `publish_interval`, `query_interval` and
`priority_group_set_interval` instead of a constant interval.