✨ (Only relevant for users of Kubebuilder as a library) - Add new cli option and allow access to underlying cli command

[beatrausch]

This PR introduces a new CLI option WithFilesystem to set the filesystem when using kubebuilder as library. Furthermore, it allows access to the underlying cobra command.

Motivations
Both features are introduced to improve testability when using kubebilder as lib. Accessing the underlying command allows to pass call arguments to in tests.

For more information see #4006

[k8s-ci-robot]

Hi @beatrausch. Thanks for your PR.

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[camilamacedo86]

I am OK with we create this one.
Just one thing, see that you can pass the FS such as

&CLI{
   fs: machinery.Filesystem{FS: afero.NewMemMapFs()},
}

as well.

[beatrausch]

Sure, but only internally.

[camilamacedo86]

/ok-to-test

[camilamacedo86]

I do not see why not add both.
Thank you for your contribution 🥇

/approved
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: beatrausch, camilamacedo86

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