✨ Provide a cli option to enable and disable completion command

[Adirio]

Description

Provide a WithCompletion CLI Option that enables adds a compeltion generation command instead of having to create it and provide it as an extra command.

Changes

• ✨ New argument type for cli.New: WithCompletion. Creating a command and providing it with WithExtraCommands should still work with the previous behavior, so this is not a breaking change, but frameworks using kubebuilder should migrate to the new approach.

[Adirio]

@camilamacedo86 This PR goes in the same direction as #1691 and #1773, moving another command out of the extra commands. I think that the API for frameworks with the new options is clearer, they only have to provide an argument instead of a full COBRA command. WDYT?

[Adirio]

A note in coverage: this PR moves part of the remaining code from cmd to pkg. As cmd was not being checked by coveralls, it says that the coverage has decreased, but in reality we just have included in the covered package part of the code that wasn't being covered by coveralls.

[camilamacedo86]

It is only missing tests.
Otherwise,
/approve

Looking for your tests for we get it merged.

[camilamacedo86]

Looking for the small nit fixes for we get it merged.
See the comments

[camilamacedo86]

/lgtm
/approve

Great work 👍

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[Adirio]

Rebased and added the tests for this option to improve coverage.

[camilamacedo86]

/lgtm