Add generation of non-periodic conda recipes

[traversaro]

This PR adds an action to generate some non-periodic conda recipes that are independent from the actual packages of the robotology superbuild. The main goal of such packages is to create metapackages that are useful for configuration.

The first example of such meta packages is vvv-school-activation, a package that is just empty and is only useful to set some environment variables used by the vvv-school and easy-peasy-robotics courses.

This will fix the following issues:

• Fix Do not add anymore <install_prefix>\share\gazebo\models to GAZEBO_MODEL_PATH ? #1563
• Fix Gazebo not finding model and world directory vvv-school/tutorial_gazebo-simple-model#1

[traversaro]

fyi @xela-95 , merging as it is required by some internal training.