Add option to allow explicit include for `ConfigOption`

[mochaaP]

Accept an optional included_params: Iterable[str] | None = None in ParamStructure.__init__.

in ParamStructure.build_param_trees, add keys to self.excluded_params if self.included_params is not None (included_params=[] is an acceptable pattern to ignore all params.)

[kdeldycke]

What would be the purpose of included_params? To be the exact reverse of excluded_params? I.e. to disregard all parameters derived from the CLI's own introspected options but the one referenced in included_params?

Or are you thinking of something completely different, i.e. a list of arbitrary parameters which are going to be recognized, alongside those derived from the CLI's own introspected options? In which case it would be clearer to name that extend_params.