Update Version Notes for SMTP Setting Change

What does this MR do and why?

As detailed in this merge request, a change was implemented in 15.10.4 and 15.11 which modifies existing behaviour of how SMTP TLS and STARTTLS settings are handled.

This MR updates the version-specific documentation to point to the updated troubleshooting documentation (the link will be correct once the MR is merged).

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