[CONFIGURATION] missing openSUSE_Leap_15.6 for OBS

[munix9 <munix9@xxxxxxxxxxxxxx>]

The configuration for openSUSE_Leap_15.6 is still missing, although 
everything necessary is already available.

There are probably two ways to implement this at the moment:

1. to implement it laboriously and elaborately in 
'gambas-package-config', or
2. use the flexibility of rpm-spec and get there faster.

I am in favor of variant 2.

What is necessary for this:
The template 'gambas3-openSUSE_Tumbleweed.spec' is already prepared for 
this, so what 'gambas-package-config' needs to do would be a
cp gambas3-openSUSE_Tumbleweed.spec gambas3-openSUSE_Leap_15.6.spec

I would rename the file 'gambas3.rpmlintrc' or 
'gambas3-openSUSE_Tumbleweed.rpmlintrc' to 'gambas3-openSUSE.rpmlintrc' 
and change it accordingly in the spec.

This results in the directory .obs/
gambas3-openSUSE_Leap_15.6.spec
gambas3-openSUSE_Tumbleweed.spec
gambas3-openSUSE.rpmlintrc