roles/nextcloud: Use Redis for caching

The Nextcloud community [recommends][0] using Redis as a cache provider,
to improve response times and file locking reliability.

roles/nextcloud/meta/main.yml

@@ -1,4 +1,7 @@
 dependencies:
+- role: redis
+  tags:
+  - redis
 - role: cert
   vars:
     cert_src: lego/_.pyrocufflink.net.crt
@@ -6,4 +9,4 @@ dependencies:
     cert_key_src: lego/_.pyrocufflink.net.key
     cert_key_dest: '{{ apache_ssl_certificate_key }}'
   tags:
-  - nextcloud
+  - nextcloud