roles/nextcloud: Switch to Fedora package

Fedora now includes a packaged version of Nextcloud.  This will be
_much_ easier to maintain than the tarball-based distribution method.
There are some minor differences in how the Fedora package works,
compared to the upstream tarball.  Notably, it puts the configuration
file in `/etc/` and makes it read-only, and it stores persistent data
separate from the application.  These differences require modifications
to the Apache and PHP-FPM configuration, but the package also included
examples to make this easier.  Since the `config.php` is read-only now,
it has to be managed by the configuration policy; it cannot be modified
by the Administration web UI.

group_vars/nextcloud.yml

@@ -6,3 +6,10 @@ pg_hba_extra:
   user: nextcloud
   address: ::1/128
   method: md5
+nextcloud_trusted_proxies:
+- 127.0.0.1
+- ::1
+nextcloud_trusted_domains:
+- nextcloud.pyrocufflink.net
+- nextcloud.pyrocufflink.blue
+- '{{ ansible_fqdn }}'