🐛 Add unlock mechanism to the kubeadm bootstrap provider

[killianmuldoon]

This fix adds logic to the Kubeadm bootstrapper that allows it to release the lock on reconciliation of control plane machines if the machine currently holding the lock can not be found.

Previously if the machine to get the lock was deleted for any reason the cluster control plane was stuck indefinitely in 'Initializing'.

Fixes #5814 (speculatively)

[vincepri]

/lgtm

[fabriziopandini]

/lgtm
@vincepri @CecileRobertMichon for a final pass

[vincepri]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vincepri

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[fabriziopandini]

/cherry-pick v1.0

[k8s-infra-cherrypick-robot]

@fabriziopandini: cannot checkout v1.0: error checking out v1.0: exit status 1. output: error: pathspec 'v1.0' did not match any file(s) known to git

In response to this:

/cherry-pick v1.0

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[fabriziopandini]

/cherry-pick release-1.0

[k8s-infra-cherrypick-robot]

@fabriziopandini: #5824 failed to apply on top of branch "release-1.0":

Applying: Add unlock if bootstrap machine holding lock does not exist
Using index info to reconstruct a base tree...
M	bootstrap/kubeadm/internal/locking/control_plane_init_mutex_test.go
Falling back to patching base and 3-way merge...
Auto-merging bootstrap/kubeadm/internal/locking/control_plane_init_mutex_test.go
CONFLICT (content): Merge conflict in bootstrap/kubeadm/internal/locking/control_plane_init_mutex_test.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Add unlock if bootstrap machine holding lock does not exist
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-1.0

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.