Separate bird/bird6 into their own containers

[jellonek]

Currently we are using a single bird container which depending on the env variables is running one or 2 daemons, then checking their liveness and if one of them died - the whole container is dying.

IMO we should instead use 2 separate containers (second one created "if needed", if ipv6 is enabled in the configuration) while the entry point for each of them should be directly bird (or bird6 in the second case), running in the foreground mode (possibly with some additional logs).

This would provide imo more k8s native way of whole thing handling (restarts) also having separately logs on consoles for both processes (e.g. right now we don't have any info why previous instance of daemon died and with which status code).