Add alias's as a :ref: target for modules

This is especially important for deprecated modules as we want to link
to those in porting guides and such.

(cherry picked from commit 8f1b5fc47b)

docs/templates/plugin.rst.j2

@@ -1,6 +1,9 @@
 :source: @{ source }@
 
 .. _@{ module }@:
+{% for alias in aliases %}
+.. _@{ alias }@:
+{% endfor %}
 
 {% if short_description %}
 {%   set title = module + ' - ' + short_description|convert_symbols_to_format %}