Add goblint configuration

Add goblint configuration

When discussing goblint on Matrix, there were some concerns
around its rules for defining properties:

 - having to explicitly track the last property ID, instead
   of including N_PROPS in the anonymous enum

 - including read-only properties in set() and write-only in get()
   adds unreachable code, which is bad for code coverage

Those were considered more important than the benefit of checking
get()/set() with `-Wswitch-enum`, so at least for now stick with
the existing property conventions.

Add a configuration that enables "legacy" style for the corresponding
rules.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/4198>