✨LeaderElection configuration as flags

[trutx]

What this PR does / why we need it:

Enables setting manager LeaderElection options via command line flags

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

Fixes #2653

I just implemented the optional settings in these two files but there's 3 other files where they could be implemented as well:

https://github.com/kubernetes-sigs/cluster-api/blob/master/controlplane/kubeadm/main.go
https://github.com/kubernetes-sigs/cluster-api/blob/master/test/infrastructure/docker/main.go
https://github.com/kubernetes-sigs/cluster-api/blob/master/cmd/example-provider/main.go

Do you think it makes sense to add the flags there too?

[k8s-ci-robot]

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[detiber]

I just implemented the optional settings in these two files but there's 3 other files where they could be implemented as well:

https://github.com/kubernetes-sigs/cluster-api/blob/master/controlplane/kubeadm/main.go

Yes, I think we'd want to expose it for the KubeadmControlPlane controller manager as well

https://github.com/kubernetes-sigs/cluster-api/blob/master/test/infrastructure/docker/main.go

Since the docker provider is mainly used for testing, I don't think there is any need to expose leader election configuration.

https://github.com/kubernetes-sigs/cluster-api/blob/master/cmd/example-provider/main.go

Same thing here, this provider should only be used during testing, so no need to expose leader election config here.

[detiber]

/ok-to-test

[chuckha]

/assign

[chuckha]

There are improvements discussed in the previous reviews that can be targeted as an add-on. Would you be able to file an issue for consolidating some kind of controller-runtime flag library we could share across controllers? Otherwise, one comment on the flag description and the rest lgtm

[vincepri]

/milestone v0.3.2

[vincepri]

We'll also need an issue in CAPA and CAPV that adds these flags there as well. I'd be also helpful to add it to this document https://master.cluster-api.sigs.k8s.io/developer/providers/v1alpha2-to-v1alpha3.html for providers to implement in the same way

[vincepri]

LGTM pending squash

[vincepri]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: trutx, vincepri

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[trutx]

Back from pseudo-holidays and all the work is done. Thanks y'all :D