cubicweb-container #3899082 provide register_* method in addition to build_* method on the configuration object [done]

Those would loose flexibility but handle case where the container root etype is added during some migration (almost) transparently. This should be enough in 99% of the time.

prioritynormal
typeenhancement
done in<not specified>
load left0.000
closed by#0083d53ce1a8 [configuration] provide register_* method in addition to build_* method
patch[configuration] provide register_* method in addition to build_* method [applied]