Allow publish_site and special_publish_directory

Some jobs in openstack/project-config (currently numerous promote
jobs) rely on being able to set values for publish_site or
special_publish_directory which get included in the target_dir path
for the parent docs promote job. Allow them to be passed through if
set.

As noted by corvus in #opendev, it's important to make sure that a
secret including one of these variables in a template var isn't used
in a job running in a pre-review pipeline, and that we trust the
people who are able to approve changes for the projects where it
runs.

Change-Id: If941922694b15ba39386d58db9e86992199017d9

playbooks/docs/promote.yaml

@@ -54,7 +54,7 @@
         target_dict: "{{ afs.targets.branch }}"
     - name: Set target path
       set_fact:
-        target_dir: "{{ target_dict.path.format(zuul=zuul) }}"
+        target_dir: "{{ target_dict.path.format(zuul=zuul, publish_site=publish_site, special_publish_directory=special_publish_directory) }}"
     - name: Adjust target path
       when: "target_dict.regex is defined"
       set_fact: