Test-infra: Add a Prow command to create branches

[zacharysarah]

What to add

Consider adding a Prow command to create new branches.

Why it matters

SIG Docs handles localizations for Kubernetes docs.

When SIG Docs adds a new localization, we add the team's leaders to a repo team with write permissions so that leaders can create long-running branches for team collaboration.

As the number of localizations increases, the number of people with write access to k/website also increases. This poses a security risk that worsens at scale. We've already seen two incidents in the past two months of contributors using write permissions to bypass Prow:

• https://github.com/kubernetes/org/pull/1293
• https://github.com/kubernetes/org/pull/1468

We need to minimize the number of people with write permissions to k/website while preserving the ability of localization teams to work on collaborative branches.

Thanks in advance for your consideration!

Additional context

#sig-docs Slack

cc @jimangel @kbarnard10 @cblecker

[zacharysarah]

/sig docs

[justaugustus]

@zacharysarah -- This is timely! Releng is discussing possibilities here: https://github.com/kubernetes/release/issues/857

cc: @kubernetes/release-engineering

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[zacharysarah]

This is still important.

/remove-lifecycle stale
/lifecycle frozen
/priority important-longterm

[cblecker]

/remove-lifecycle frozen

We haven't decided if/how we would do this, so it doesn't really qualify for frozen.

I'm not sure what the workflow would even look like for this.. we don't really do repo-scoped commands. They are all issue or PR scoped.

[stevekuznetsov]

If we implement branch creation as a plugin, we can just enable the plugin on a single repo.

[cblecker]

@stevekuznetsov That's not what I mean. I mean where would you issue the command to create a branch?

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[jimangel]

/remove-lifecycle stale

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