Add fields to the server status from server descriptors

We need some fields from server descriptors to be added to the server status so we do not need to make a DB join when building responses in the API. See: networkstatusapi#8 (comment 2948959)

-- This is for the relay query
sd.exit_policy as exit_policy_summary
sd.ipv6_default_policy
sd.contact
sd.bandwidth_rate
sd.bandwidth_burst
sd.bandwidth_observed
sd.is_hibernating
sd.dir_port

-- This is for bridge query
sd.overload_general_timestamp