Feature: isType assertition

[rquinio1A]

I didn't find a way to assert the type of a specific value (string, number, boolean, ...)
My use case would be to check that all K8s container env values have type string, otherwise it causes error like "cannot convert int64 to string".

Something like:

- isType:
    path: spec.template.spec.containers[0].env[value]
    type: string

[quintush]

Hello @rquinio1A, @d3adb5,

Thanks for the feedback and the initial PR.
The isType assertion is a valid addition to the asserts.

Will try to provide feedback on PR as soon a possible.

Greetings,
@quintush