Add kubeadm_join_phases_skip variable

[necatican]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Allows users to be able to skip some phases in the join_phase using kubeadm_join_phases_skip.

We already have a variable (kubeadm_init_phases_skip) to skip init phases. Another one for the join phases would be beneficial.

Which issue(s) this PR fixes:

Fixes #8066

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Add the ability to skip some phases in the kubeadm join_phase using `kubeadm_join_phases_skip`

[k8s-ci-robot]

Hi @necatican. Thanks for your PR.

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[cristicalin]

To keep this inline with the kubeadm_init_phases_skip_default naming option, maybe it's better to follow the same logic and expose kubeadm_join_phases_skip_default as the user facing variable and compile kubeadm_join_phases_skip from joining a currently empty list (with the option to extend it later if we discover the need) with the contents of kubeadm_join_phases_skip_default.

👍 for spotting this issue

[necatican]

To keep this inline with the kubeadm_init_phases_skip_default naming option, maybe it's better to follow the same logic and expose kubeadm_join_phases_skip_default as the user facing variable and compile kubeadm_join_phases_skip from joining a currently empty list (with the option to extend it later if we discover the need) with the contents of kubeadm_join_phases_skip_default.

👍 for spotting this issue

Thank you for the ideas and for the better documentation. 🙂 I've added the kubeadm_join_phases_skip_default variable.

[floryut]

/ok-to-test
Good idea 👍

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floryut, necatican

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[oomichi]

/lgtm