Use kube_config_dir for kubeconfig

[oomichi]

What type of PR is this?

/kind bug

What this PR does / why we need it:

The path of kubeconfig should be configurable, and its default value is /etc/kubernetes/admin.conf.
Most paths of the file are configurable but some were not.
This make those configurable.

Does this PR introduce a user-facing change?:

Use `kube_config_dir` for kubeconfig instead of hard path in multiple plays

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[floryut]

I guess we could also update paths in

kubespray/roles/kubernetes/control-plane/tasks/kubeadm-setup.yml

Lines 153 to 164 in 2211504

	{{ bin_dir }}/kubeadm --kubeconfig /etc/kubernetes/admin.conf token delete {{ kubeadm_token }} || :;
	{{ bin_dir }}/kubeadm --kubeconfig /etc/kubernetes/admin.conf token create {{ kubeadm_token }}
	changed_when: false
	when:
	- inventory_hostname == groups['kube_control_plane']|first
	- kubeadm_token is defined
	- kubeadm_refresh_token
	tags:
	- kubeadm_token
	- name: Create kubeadm token for joining nodes with 24h expiration (default)
	command: "{{ bin_dir }}/kubeadm --kubeconfig /etc/kubernetes/admin.conf token create"

And in

kubespray/roles/kubernetes/control-plane/tasks/kubeadm-upgrade.yml

Line 65 in 2211504

--kubeconfig /etc/kubernetes/admin.conf

[oomichi]

@floryut Thank you for your review, that is a nice point.
I updated the pull request based on your point.