Add jobs and config for gardener-extension-provider-equinix-metal

[RiRa12621]

/kind enhancement
/kind test

What this PR does / why we need it:
We would like to use prow for gardener-extension-provider-equinix-metal related tests as well to unifi the experience

[RiRa12621]

/assign @acumino
obey the bots

[gardener-ci-robot]

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/lifecycle stale

[gardener-ci-robot]

The Gardener project currently lacks enough active contributors to adequately respond to all PRs.
This bot triages PRs according to the following rules:

• After 15d of inactivity, lifecycle/stale is applied
• After 15d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 7d of inactivity since lifecycle/rotten was applied, the PR is closed

You can:

• Mark this PR as fresh with /remove-lifecycle rotten
• Close this PR with /close

/lifecycle rotten

[oliver-goetz]

/remove-lifecycle rotten

[oliver-goetz]

It's nice that you plan to enable prow for the equinix metal extension 🙂
I'm sorry that the review took so long.

There are a couple of things to be changed apart from my review comment:

• you might want to enable branch protection similar to how it is done for cert-management as both repos still use concourse jobs.
• please add the label sync for your repository, again similar to cert-management (ref1, ref2)
• You could add your repository to the config of the lifecycle bot (ref)
• You should add OWNERS and OWNER_ALIASES files to the root of your repository. There are examples how they look like in this repository.
• If you like you can add your repo to the renovate config and run make generate-prow-deployments afterwards

[oliver-goetz]

Could you rebase please, because we deduplicated the tide config with #2609

[gardener-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[gardener-prow]

Adding label do-not-merge/contains-merge-commits because PR contains merge commits, which are not allowed in this repository.
Use git rebase to reapply your commits on top of the target branch. Detailed instructions for doing so can be found here.

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