Initial CCM migration implementation for OpenStack

[xmudrii]

What this PR does / why we need it:

This is the very first step of the CCM/CSI migration implementation. The purpose of this PR is to get some idea of how the migration implementation will be shaped. Note that the implementation might get changed until the migration is not fully implemented.

There are currently the following limitations:

• Only the CCM migration is supported. CSI migration will be done in a follow-up PR
• Only OpenStack is supported. Other cloud providers will follow up in KubeOne 1.4+
• This is only partial migration (to be explained later). Completing migration will be implemented in a follow-up PR along with CSI migration

The migration is triggered by the following command:

kubeone migrate to-ccm-csi -m kubeone.yaml -t .

Note: The command is currently hidden and should not be used until the migration is not fully implemented.

The migration works in the following way:

• Run a bunch of checks to make sure it makes sense to migrate
  • For example, we ensure that the cluster is not already running external CCM, that .cloudProvider.external is enabled, that the cloud provider is supported
• Regenerate the configuration files, including the kubeadm config files
• Force upgrade the control plane nodes
  • This is done to apply the required flags for API server and controller-manager
  • Alternative approach would be to manually edit static pod manifests. However, the current (upgrade) approach seems easier and I don't see any benefits to manually editing manifests
  • As mentioned at the beginning, at this point we're doing partial migration, which means:
    • --cloud-provider and --cloud-config flags are kept until the CSI migration is not complete
    • CCM-related controllers are disabled in kube-controller-manager
• Ensure resources
  • We'll deploy external CCM and CSI at this step
  • machine-controller-webhook is configured with -node-external-cloud-provider flag

After the initial migration is done, users are expected to:

• Rotate all their machine-controller-managed worker nodes
• Complete migration by running:

  kubeone migrate to-ccm-csi --complete -m kubeone.yaml -t .
  

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
xref #1451 #1452

Does this PR introduce a user-facing change?:

NONE

/assign @kron4eg

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Git tree hash: 29bcd84e5be0f6668eef0742dc8e18fb338f7149