ssl: also support the SSLCertificateChainFile required by some providers

apache/vhosts/standard.tmpl

     {%   if site.get('SSLCertificateKeyFile') %}
     SSLCertificateKeyFile {{ site.SSLCertificateKeyFile }}
     {%   endif %}
+    {%   if site.get('SSLCertificateChainFile') %}
+    SSLCertificateChainFile {{ site.SSLCertificateChainFile}}
+    {%   endif %}
     {% endif %}
 
     {% for path, dir in site.get('Directory', {}).items() %}

pillar.example

 
       SSLCertificateFile: /etc/ssl/mycert.pem # if ssl is desired
       SSLCertificateKeyFile: /etc/ssl/mycert.pem.key # if key for cert is needed or in an extra file
+      SSLCertificateChainFile: /etc/ssl/mycert.chain.pem # if you require a chain of server certificates file
 
       Directory:
         # "default" is a special case; Adds ``/path/to/www/dir/example.com``