Template upgrade guide 2.11 -> 2.12 missing note on upgrading external databases

When performing upgrade of template based 3scale 2.11 with external mysql or external postgresql there is missing note saying that the customer must upgrade their external mysql to mysql 8 with additional configuration (the same as it is for operator 3.2.1. Upgrading the external MySQL version to 8.0).

Or when they are upgrading their template 3scale 2.11 deployment with external postgres they must upgrade their external postgres to postgres 13 (the same as it is for operator 3.2.3. Upgrading the external PostgreSQL to version 13).