Avocado + Avocado-VT release and compatibility tracking

[clebergnu]

There needs to be a way to define the cycle of Avocado-VT development phases which are not bound to be guaranteed compatibility with Avocado.

A proposal for those cycles was sent out in the past, but due to a lack of a tool or mechanism, it was not applied properly. One example of it being applied, though can be seen here:

CI: reinstate the waiver of failures with latest Avocado
    
    This marks the point where the latest development (HEAD of master
    branches) of Avocado-VT and Avocado are not guaranteed to be
    compatible (to he extent that is being tested here).
    
    The goal here is to allow for Avocado core changes that will affect
    plugins without breaking Avocado-VT development.  The following is the
    proposed development cycles for Avocado:
    
    1) Avocado 101.0 - bug fixes, improvements and core changes (possibly
       affecting plugins)
    2) Avocado 102.0 - bug fixes, improvements and core changes (possibly
       affecting plugins)
    3) Avocado 103.0 (LTS) - bug fixes, compatibility and usability
       improvements only.
    
    The compatibility check will be restored at the beginning of the
    Avocado 103.0 development cycle, resulting in a Avocado-VT and Avocado
    release that are compatible.

The definition of done is a clear mechanism that influences the release process producing Avocado-VT releases that are guaranteed to be compatible with Avocado.