extensions_manager: Introduce typed callbacks for extensions_manager

This MR introduces typed callbacks as an alternative to the variadic argument pf_control

The rationale behind this MR is the same as in MR !3200 (merged).

The goal by introducing typed callbacks is to have a safer interface to plug into but also to move away from the mess around va_list (each compiler defines va_list differently, needs to have va_arg everywhere, limited support in safer languages, prone to errors, ...).

The driving factor behind this is to permit programming languages that don't have support for implementing a function that uses va_list to still be able to implement those callbacks.