Support case insensitive name matching

[Alienmario]

This is a simple request for case insensitive name matching for commands / options.

I want to use CliNameCasingConvention.CamelCase for better help readability, but still accept lowercase inputs.

[calacayir]

This because System.CommandLine itself is case sensitive. You can manually add aliases for this, however we can add all lowercase version of the alias automatically (though we can't handle mixed case versions).

[Alienmario]

Perhaps you could add an aliasing variant of NameCasingConvention (NameCasingConventionAliases?). Anyways, since System.CommandLine doesn't support this, feel free to close if you feel like this is overreaching.

[vpenades]

if casing convention is intended for file names, I would recomend using System.IO.MatchCasing enumeration.

It has case sensitive, case intensitive, and platform default which would be the default value.