Added option to configure dependencies for kubelet.service

[ledroide]

What type of PR is this?:

/kind feature

What this PR does / why we need it:

It helps to solve issues related to kubelet systemd service dependencies, such as nfs and rpc-statd issues.

Special notes for your reviewer:

Tested :

• add kubelet_systemd_wants_dependencies: ["rpc-statd.service"] in inventory file group_vars/k8s_cluster/k8s-cluster.yaml
• apply full cluster.yml playbook
• on servers, the line Wants=rpc-statd.service is correctly added to [Unit] section
• systemctl stop rpc-statd
• systemctl restart kubelet
• systemctl status rpc-statd
• result OK : rpc-statd is started

Does this PR introduce a user-facing change?:

New variable documented in docs/variables.md. As long as this variable is not set, nothing changes.

Added option to configure dependencies for kubelet.service

[k8s-ci-robot]

Hi @ledroide. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[yankay]

/ok-to-test

[yankay]

Thanks @ledroide
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ledroide, yankay

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[ant31]

/lgtm