Deploy external Cloud Controller Manager (CCM) if Provider.External is set

[xmudrii]

Currently if Provider.External is set to true it's user's responsibility to deploy the external CCM. We should consider deploying the external CCM ourselves because currently we're running into many edge cases:

• if --cloud-provider=external is set on Kubelet all nodes (including control plane nodes) will stay uninitialized until CCM is not deployed,
• this prevents components to be deployed, including system components such as CoreDNS,
• without CoreDNS, DNS functionality will not be available in the cluster and we can't create worker nodes,
• for cloud providers without in-tree CCMs, not all information about nodes is populated, for example IP addresses

When deploying CCM ourselves we deny user from choosing what CCM version they want to run, however we're gaining more control and we can ensure that such CCM version is working on KubeOne clusters.

At this point, this issue is blocked until machine-controller doesn't implement features needed for the external CCM to work as expected.

/kind feature
/lifecycle blocked

UPDATE:
Need to reference machine-controller credentials secret from CCM deployment.

[xmudrii]

Blocked by machine-controller supporting external CCM

[kron4eg]

--cloud-provider=external is merged in kubermatic/machine-controller#470