CLI config provider defaults always override ENV about flow

[osdrv]

Initially, while working on the registry code, I made a wrong assumption: a provider that registered itself, can always serve this config key. This turns out to be a wrong idea: providers are registered at the start up time, but the runtime env is never known in advance at this stage, so, some providers might have no data to serve. Based on my assumption, I took a decision to use a bin heap as the primary data structure. It seems the most legitimate behavior in this context would be to use a per-config-key list of providers, prioritized based on their weight and the config resolved within O(N) steps until one of the providers returns lookup ok == true.
the lookup propagation would look like:

client fetches a value for a config key:
    registry gets prioritized list of providers serving the key
        registry1 returns _, false
        registry2 returns _, false
        ...
        registryN returns v, true
    registry returns v, true