Fix redirect links in jenkins/README.md

[tuminoid]

The link checker found URLs that redirect to new locations. These should be updated to point directly to the correct URLs:

Redirects in jenkins/README.md

Current URL	Redirects To
https://kubernetes.slack.com/messages/CHD49TLE7	https://kubernetes.slack.com/?redir=%2Fmessages%2FCHD49TLE7
https://www.citycloud.com/	https://cleura.com/
https://www.nordix.org/	https://openinfraeurope.org/

Related to #1175

/triage accepted
/help
/good-first-issue

[metal3-io-bot]

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Details

In response to this:

The link checker found URLs that redirect to new locations. These should be updated to point directly to the correct URLs:

Redirects in jenkins/README.md

Current URL	Redirects To
https://kubernetes.slack.com/messages/CHD49TLE7	https://kubernetes.slack.com/?redir=%2Fmessages%2FCHD49TLE7
https://www.citycloud.com/	https://cleura.com/
https://www.nordix.org/	https://openinfraeurope.org/

Related to #1175

/triage accepted
/help
/good-first-issue

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