Migrate prow domains to kcp.io

[embik]

We're currently still hosting Prow domains under the *.kdp.k8c.io subdomain, we should migrate those to kcp.io. I believe we just need to open CNCF service desk tickets to get DNS entries.

[kcp-ci-bot]

Issues go stale after 90d of inactivity.
After a furter 30 days, they will turn rotten.
Mark the issue as fresh with /remove-lifecycle stale.

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/lifecycle stale

[embik]

/remove-lifecycle stale