Configuration should be stored in Redpanda

[rkruze]

All configuration for Redpanda is currently stored in configuration files normally stored in the /etc/redpanda directory. Ideally, most of the configuration options needed should be stored in Redpanda itself. This would make it possible to quickly push out configuration information to the whole cluster. This could be done with something like a compacted topic.

One could envision just a list of seed servers, advertised address, and data directory as the only configuration options local to the instance, with everything else being global and saved in Redpanda centrally. It would then make sense to use something like rpk to configure the parameters stored in Redpanda.

[rkruze]

duplicate of #245