[sidnei] The 'all_services' config now supports a static list of servers to be used *in addition* to the ones provided via relation. [sidnei] When more than one haproxy units exist, the configured service is upgraded in-place to a mode where traffic is routed to a single haproxy unit (the first one in unit-name order) and the remaining ones are configured as 'backup'. This is done to allow the enforcement of a 'maxconn' session in the configured services, which would not be possible to enforce otherwise. [sidnei] Changes to the configured services are properly propagated to the upstream relation.