cluster(lb): fix load balancer stuck degraded during bootstrap

[mweibel]

During initial cluster bootstrap the load balancer could get stuck in degraded or error and never recover on its own. Two things combined to cause this:

• The health monitor was created before any control-plane node existed. With a monitor but no healthy members, the LB reports degraded/error.
• The reconciler never requeued a non-running LB, so it never observed the LB recovering once the control-plane nodes came up. This was especially the case if it took a bit of time until control plane nodes were available.

Changes:

1. Requeue every 10s while the LB is pending (degraded/error)
2. Defer creating the health monitor until the control plane is initialized (at least one control-plane node up).
3. Move health monitor reconciliation to the end of reconcileNormal, after the load balancer and floating IP, since it depends on both being set.

Also fixes the cloudscaleMachineToCluster watch mapping, which filtered on the wrong label (MachineControlPlaneNameLabel instead of MachineControlPlaneLabel) and so never enqueued on control-plane machine changes.