roles/named: Deploy BIND DNS server

The *named* role configures the BIND DNS server on managed nodes. It
writes `/etc/named.conf`, using a template that supports most of the
commonly-used options. The configuration can be augmented by other
templates, etc. by specifying file paths in the `named_options_include`
or `named_global_include` variables, both of which are lists.

roles/named/defaults/main.yml

@@ -0,0 +1,14 @@
+named_listen:
+- port: 53
+  addresses:
+  - 127.0.0.1
+named_listen_v6:
+- port: 53
+  addresses:
+  - ::1
+named_allow_query:
+- localhost
+named_recursion: true
+named_dnssec: true
+named_dnssec_validation: true
+named_options_include: '{{ named_default_options_include }}'