Add service#subscribe to listen for specific events
Instrument Net::LDAP::Connection#search
Extract instrumentation for reuse

Allows us to use the same method for Net::LDAP and Net::LDAP::Connection.
Instrument Net::LDAP#search
Capture search result in instrumentation
Add lib/net/ldap/instrumentation.rb to Manifest, gemspec
Spec out Net::LDAP#search instrumentation
Spec more consistently, separate
Spec out search.net_ldap_connection event