Improve "migrating from modules development" documentation

[lcaouen]

In the documentation https://epics-extensions.github.io/EPNix/nixos-25.05/ioc/user-guides/deprecations/migrating-from-modules-development.html

• Would be nice to "emphasize" the difference between the before and after sections.
• Add precision to "Add your EPICS support modules dependencies into propagatedBuildInputs"
• Add EPNIX_MODBUSSUPPORTTOP has been changed to MODBUS_SUPPORT_TOP

[agaget]

• error here, it should be ioc.nix not flake : https://epics-extensions.github.io/EPNix/dev/ioc/user-guides/deprecations/migrating-from-modules-development.html#id10
• epnix.support.mySupportModule doesn't work, you should have mySupportModule only and also as an argument
• Miss mentions about the fact that we need to also migrate any inputs we use to 25-05 before upgrading the top