Add an option to create menu in the QGIS browser

[Guts]

Feature description

In addition to the possibility of adding a menu in the QGIS menu bar and in the "Add a layer menu", we propose to add a new location in the project's settings.

It is proposed to build the tree structure in the Browser (corresponding to the "menus" in the plugin) under a single LMFP entry:

Additional context

This feature is similar to what the IDG plugin does: https://github.com/geo2france/idg-qgis-plugin/.

This feature request is formulated from Agences de l'Eau and ported by Oslandia.

[Guts]

Duplicate of #107