Cluster-api: Avoid linking to the "master" branch of Kubernetes repositories

[fabriziopandini]

The the "master" -> "main" branch rename can happen in k8s repositories,
in the near future, which will break the links in this repository.

We can avoid referencing a "master" branch if the URL:
"https://git.k8s.io/repo" is used instead of
"https://github.com/kubernetes/{blob|tree}/master"

/kind cleanup
/kind documentation
/priority backlog

[fabriziopandini]

/milestone Next
This can be merged whenever it is ready

/good-first-issue

[k8s-ci-robot]

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In response to this:

/milestone Next
This can be merged whenever it is ready

/good-first-issue

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[vincepri]

Duplicate of https://github.com/kubernetes-sigs/cluster-api/issues/3280 ?

[arghya88]

I can work on this if that is okay.

[fabriziopandini]

Duplicate of #3280 ?

Not really, #3280 is about changing the main branch for this repo, this issue is about getting ready for the branch being changed in k/*

[fabriziopandini]

I can work on this if that is okay.

Sure!
/assign @arghya88
/lifecycle active