Provide high-level interface to set favicon

[Tectu]

Provide a high-level interface (most likely in zim::controller) to set a favicon.

This function should accept a filesystem path to the corresponding favicon.ico file and automatically register the corresponding GET /favicon.ico endpoint.

Alternatively, a filesystem path could be provided to the controller configuration (zim::controller::configuration). Upon initialization of the controller (zim::controller::init()) the controller could check whether a valid filepath was provided and create the corresponding GET /favicon.ico endpoint as needed.