Add install-sysconfdir=no-samples option for (non-)installation of sample configs

By default, systemd installs various sample configuration files
containing commented-out defaults. Systems seeking to minimize the
number of files in /etc may wish to install directories and
configuration files that have semantic effects, but not install not
commented-out sample configuration files.

Turn install-sysconfdir into a multi-valued option, with a "no-samples"
value to skip installing sample-only configuration files.

src/oom/meson.build

@@ -29,7 +29,7 @@ if conf.get('ENABLE_OOMD') == 1
         install_data('org.freedesktop.oom1.service',
                      install_dir : dbussystemservicedir)
 
-        if install_sysconfdir
+        if install_sysconfdir_samples
                 install_data('oomd.conf',
                              install_dir : pkgsysconfdir)
         endif