Clarify workaround possibility in Kerberos setup

What does this MR do?

In MR !69945 (merged) a note was added claiming that GitLab CI will not work at all on a Kerberos integrated instance.

This can be worked around if the integration is setup to use separate ports.

While the choice of doing this depends on the administrators because it involves certain overheads in instructing users to use one port over other in specific scenarios, the workaround should allow GitLab CI/CD to continue to work over the default HTTP authentication ports.

This change adds some clarifications on:

• What the fix in Git 2.4 truly supports
• What is necessary for Kerberos integration to work with GitLab CI/CD

Related issues

!69945 (merged)

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