cmake magic for documentation

[Harald Sitter]

hola!

Currently releaseme pulls off a whole bunch of tricks to get first
level conditional magic working for documentation.

Since you probably have no clue what that means. Go looky here:
https://cgit.kde.org/plasma-workspace.git/tree/doc/CMakeLists.txt

This cmake file has a conditional on effectively installing the polkit
documentation. Now that is technically lovely and awesome, but it
makes dealing with translations super awkward.
Namely translations themselves do not have cmakelists, so what ends up
is either the release tool generating the cmakelists OR kdoctools
figuring things out at configure time. So, while this conditional
works for en_US it has 0 impact on any translations.

Releaseme has special magic to handle this, it's super craft, hard to
maintain and somewhat preventing us from moving to letting kdoctools
handle this.

So. Can we drop this sort of stuff and just accept that we always
install all docs?

HS