roles/postgresql-server: Support SSL configuration

This commit adds a task to generate a PostgreSQL configuration file from
a template.  Previously, the default configuration file generated by
`initdb` was sufficient, but in order to enable SSL connections, some
changes to it are required.

Naturally, SSL connections require a server certificate, so the
*postgresql-server* role will now also copy certificate files to the
managed node, if any.

roles/postgresql-server/defaults/main.yml

@@ -1,3 +1,4 @@
 pgdata_dir: /var/lib/pgsql/data
 pg_locale: en_US.UTF-8
 pg_ident: []
+pg_ssl: false