po: add basic fedora.zanata.org configuration

This is in response to https://bugzilla.redhat.com/show_bug.cgi?id=1320812.
There is a chance that we will get additional translations through
zanata, so let's try that. To upload .pot and current translations:

$ ninja -C build systemd-pot
$ zanata-cli push
$ zanata-cli push  --push-type trans --trans-dir po

zanata.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<config xmlns="http://zanata.org/namespace/config/">
+  <url>https://fedora.zanata.org/</url>
+  <project>systemd</project>
+  <project-version>master</project-version>
+  <project-type>gettext</project-type>
+  <src-dir>po</src-dir>
+  <trans-dir>po</trans-dir>
+</config>