[Ftr] Allow flags to be true when the value is not specified

[bkmeneguello]

Is your feature request related to a problem? Please describe.
Boolean flags should not require a value, this is very nonstandard in relation to other CLI

Describe the solution you'd like
I want a flag to be considered true if it's present, so xxx --flag should be true instead of xxx --flag=Y

Describe alternatives you've considered
My workaround to this feature is to use :with-flag but this creates the [no-]flag alternatives which pollute my options, since false is the default.

[bkmeneguello]

For example, I need to create a pass-through CLI to parse kubectl options, it must be able to replace the original executable (a wapper), but :flag options do not work the same way