debinstall #119789 make it possible to configure the header of the generated Release file [validation pending]

For example, I'd like to be able to define the "Suite" of a given repo.

prioritynormal
typeenhancement
done in2.7.0
load1.000
load left0.000
closed by#8be74904cd12 [publish] use a persistent header for generated apt.conf (closes #119789)
patch[publish] use a persistent header for generated apt.conf (closes #119789) [applied]