Fixing typo in Fleet port requirements

[jeanfabrice]

• Fleet port is wrong. 5601 is Kibana default port
• "Fleet" doesn't really make sense
• Neither Elastic Agent nor Fleet Server connect to Kibana port

[github-actions]

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[mergify]

This pull request does not have a backport label. Could you fix it @jeanfabrice? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-/d./d is the label to automatically backport to the /d./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.