Fix upgrade procedure with kubeadm preflight flags

[iagusev]

Description

Fixed missing ignorePreflightErrors flag during upgrade of non-initial control-planes and worker nodes.
Previously, only the first control-plane used it, which could cause upgrade failures on other nodes.

Solution

Added unified flags variable:

flags = ("--certificate-renewal=true "
         f"--ignore-preflight-errors='{cluster.inventory['services']['kubeadm_flags']['ignorePreflightErrors']}' "
         f"--patches=/etc/kubernetes/patches")

Updated upgrade_other_control_planes() and upgrade_workers() to use:

sudo kubeadm upgrade node {flags} && ...

How to apply

Run standard upgrade procedure.
No manual steps required.

Test Cases

Verified upgrade on CentOS8 cluster with preflight warnings.
Before: upgrade failed on non-initial nodes.
After: upgrade completed successfully on all nodes.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• There is no breaking changes, or migration patch is provided
• Integration CI passed
• Unit tests. If Yes list of new/changed tests with brief description
• There is no merge conflicts