Issue 4687 - Add Context Function get_pages_metadata to Test Site

tests/test_site/pages/sitemap.tmpl

 template = empty 
 product = foo
 title = test_metadata
-tags = popular, bar
+tags = [popular, bar]
 <h1> Unfiltered </h1>
 <ul>
     {%- for unfiltered_page in get_pages_metadata() -%}
-<li>{{ unfiltered_page }} </li>
+        <li>title : {{ unfiltered_page['page']}} </li>
 {%- endfor %}
 </ul>
 
 <h1> Filtered </h1>
 <ul>
-{%- for page in get_pages_metadata({'tags': 'popular, bar'}) -%}
-<li> {{ page }} </li>
+    {%- for filtered_page in get_pages_metadata({'tags': ['popular', 'bar']}) -%}
+        <li>title : {{ filtered_page['page'] }} </li>
 {%- endfor %}
 </ul>
+
+<h1> String Filter For Listy Option </h1>
+<ul>
+    {%- for filtered_page in get_pages_metadata({'tags': 'popular'}) -%}
+        <li>title : {{ filtered_page['page'] }} </li>
+{%- endfor %}
+</ul>