Config system ignores unknown config values silently

[Bultako]

I have found that Tools do not always capture bad or invalid arguments. Some examples below.

MyTool --foo=True
WARNING [MyTool] (loader/load_config): Unrecognized alias: '--foo=True', it will probably have no effect.
INFO [MyTool] (tool/initialize): ctapipe version 0.8.0.post31+gite99e39c

MyTool --Foo=True
WARNING [MyTool] (loader/load_config): Unrecognized alias: '--Foo= True', it will probably have no effect.
CRITICAL [MyTool] (application/catch_config_error): Bad config encountered during initialization:
CRITICAL [MyTool] (application/catch_config_error): Invalid argument: '--Foo=1'

MyTool --foo.bar=True
INFO [MyTool] (tool/initialize): ctapipe version 0.8.0.post31+gite99e39c

MyTool --Foo.bar=True
INFO [MyTool] (tool/initialize): ctapipe version 0.8.0.post31+gite99e39c

I guess this could produce an unexpected behavior of the Tool if a misspelled argument is passed together with a config file having the right argument name, which will turn out sometimes in a silent execution of the Tool.

[maxnoe]

Yes, it seems non-top-level config options are just silently ignored.

I could have sworn I already opened this issue, but I could not find it. So maybe I forgot to open it.

[kosack]

perhaps add this to #1406 (reqs for a new config system).

[kosack]

also related to https://github.com/ipython/traitlets/issues/145