This commit renames the `service_violation` column that can be added via
a policy script to `failed_service`. This expresses the intent of it
better - the column contains services that failed and were removed after
confirmation.
Furthermore, the script is fixed so it actually does this - before it
would sometimes add services to the list that were not actually removed.
In the course of this, the type of the column was changed from a vector
to an ordered set.
Due to the column rename, the policy script itself is also renamed.
Also adds a NEWS entry for the DPD changes.
This introduces ian options, DPD::track_removed_services_in_connection.
It adds failed services to the services column, prefixed with a
"-".
Alternatively, this commit also adds
policy/protocols/conn/failed-services.zeek, which provides the same
information in a new column in conn.log.
