feat(config): Start warning on unknown flags or config (under loglevel=warn)

[darcyclarke]

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1. gar/invalid opts nopt#179
   +0
2. consider warning on all aliases in nopt
3. [FEATURE] Add a handler for *unknown* options, analogous to invalidHandler nopt#41
   Enhancement +1
   

[wraithgar]

we should also warn when npm is "helpfully" allowing for abbreviated versions of any config item, with the goal of eventual removal in a future major

$ npm config ls -a -- --bef=2010-10-10|grep before
$ npm config ls -a --bef=2010-10-10|grep before
before = "2010-10-10T00:00:00.000Z"