Add upgrade guide to 13.11 to avoid faulty migration

What does this MR do and why?

A migration was introduced in 13.11 !59270 (merged), which incorrectly sets a column value and could lead to potential data loss.

This has been fixed on SaaS, but there are still self-managed users who are on versions < 13.11 who may upgrade to this version.

Sicne this version is far out of the maintenance policy, this MR adds upgrade guide to 13.11 to patch the migration in order to avoid potential data loss.

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Related to #361396 (closed)