Initial commit: minimal CAPI bootstrap provider for ignition configs

A CAPI bootstrap provider that references a pre-existing Secret
containing an ignition config (e.g., from the OpenShift Machine
Config Server). Satisfies the CAPI bootstrap contract by copying
the Secret data and reporting ready.

Designed to work with 5-Spot ScheduledMachines and CAPLV on
OpenShift clusters where a CAPI bootstrap provider is needed
but KubeadmConfig is incompatible.

Signed-off-by: Anthony Green <green@redhat.com>