🌱 Stop gap for kubeadm types removal

[fabriziopandini]

What this PR does / why we need it:
This PR implements a stop-gap solution for kubeadm types removal explicitly designed for back-porting on the v1alpha3 branch.

The solution implemented is described in the #4170 (and more specifically this is alternative 2 for v1alpha3).

After this will be backported, a proper conversion mechanism is going to be implemented in v1alpha4 only (also described in the proposal).

Which issue(s) this PR fixes:
Fixes #

/milestone v0.4.0
/hold
For the CAEP to merge

@vincepri

[vincepri]

sigs.k8s.io/cluster-api/bootstrap/kubeadm/types/v1beta1
  Incompatible changes:
  - ConfigurationToYAML: changed from func(k8s.io/apimachinery/pkg/runtime.Object) (string, error) to func(k8s.io/apimachinery/pkg/runtime.Object, string) (string, error)
  - GetCodecs: removed
  - MarshalToYamlForCodecs: removed
  Compatible changes:
  - K8sVersionToKubeadmAPIGroupVersion: added

We should keep those exported functions, and Add a new ConfigurationToYAML

[vincepri]

Minor comments, otherwise lgtm

[vincepri]

I don't think this change requires the proposal to be merged?

[fabriziopandini]

I don't think this change requires the proposal to be merged?

As much test cycles we can get, the better!
The proposal is out from some time now and AFAIK there are no blockers. Also this PR was discussed in the last Meeting, and no objection were raised there/on this PR, so I guess we are fine.

[fabriziopandini]

/hold cancel

[fabriziopandini]

@CecileRobertMichon @detiber any objection to get this work moving so we can get as much a possible test cycles on this change?

[vincepri]

/lgtm

/assign @CecileRobertMichon
for final approval

[detiber]

/approve
/hold
adding hold in case @CecileRobertMichon still wanted to review, feel free to remove if that is not the case.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[CecileRobertMichon]

/hold cancel

sorry completely missed the ping on this