Make use of HTTP and HTTPS proxy configurable

Created by: jschoone

As an SCS Operator, I want to be able to configure the use of a corporate proxy in my Kubernetes clusters created by ClusterAPI. Specifically I want to be able to specify the proxy settings in the ClusterAPI configuration and have these settings propagated to all nodes in the cluster during provisioning.

• setup test proxy
• introduce new config variable http_proxy

Part1: mgmt host (#620 )

• /etc/profile mgmt host
• apt for cloud-init
• provisioning scripts
• docker client mgmt host
• docker daemon mgmt host

Part2: worker nodes

• /etc/profile worker?
• containerd worker
• kubelet worker

Part3: controlplane

• /etc/profile controlplane?
• containerd controlplane
• kubelet controlplane nodes

For now, i crossed /etc/profile from the list for the k8s-nodes. As /etc/profile is mostly used for login-shells. cluster-api managed-nodes are either created and provisioned automatically or deleted. Manual configuration via a login-shell (that would need proxy settings to be present in /etc/profile) is therefore unnecessary.