Clarify unsupported GSSAPI mechanism troubleshooting

What does this MR do and why?

This MR works to address the #372720 issue by:

• Adding "follow the 'use a dedicated port'" tip to the unsupported GSSAPI mchanism troubleshooting subsection
• Organizing the unsupported GSSAPI mchanism troubleshooting subsection (as there are now four tips and it can be a bit tough to read)

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