move roles, files and templates dirs out of playbook dir into root dir

Because of how Ansible local relative search paths work, the global
"files" and "templates" directories need to be next to the playbooks.
However its not intuitive to look into the "playbooks" directory to find
the files and templates for a host.
Therefore move them out of the "playbooks" directory into the root
directory and add symlinks so everything still works.

Similarly for local roles, they also need to be next to the playbooks.
So for a nicer structure, move the "roles" directory out into the root
directory as well and add a symlink so everything still works.

Also see:
https://docs.ansible.com/ansible/latest/playbook_guide/playbook_pathing.html#resolving-local-relative-paths
https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_reuse_roles.html#storing-and-finding-roles

roles/nextcloud/meta/argument_specs.yaml

@@ -0,0 +1,63 @@
+argument_specs:
+  main:
+    options:
+      nextcloud__version:
+        description: The version label to use for the Nextcloud Docker image.
+        type: str
+        required: true
+      nextcloud__postgres_version:
+        description: The version label to use for the PostgreSQL Docker image.
+        type: str
+        required: true
+      nextcloud__nginx_version_spec:
+        description: The version spec. to pass to nginx to use for the nginx version spec.
+        type: str
+        required: false
+        default: ""
+      nextcloud__certbot_version_spec:
+        description: The version spec. to pass to certbot to use for the certbot version spec.
+        type: str
+        required: false
+        default: ""
+      nextcloud__fqdn:
+        description: The FQDN to use for Nextcloud.
+        type: str
+        required: true
+      nextcloud__data_dir:
+        description: The directory where to store the Nextcloud data.
+        type: str
+        required: true
+      nextcloud__admin_password:
+        description: The password to use for the Admin user.
+        type: str
+        required: true
+      nextcloud__extra_configuration:
+        description: Additional nextcloud configuration.
+        type: str
+        required: false
+        default: ""
+      nextcloud__use_custom_new_user_skeleton:
+        description: >-
+          Enable to make use of the given custom new user skeleton directory.
+        type: bool
+        required: false
+        default: false
+      nextcloud__custom_new_user_skeleton_directory:
+        description: >-
+          Path of to a custom new user skeleton directory to be used by this
+          role via ansible.builtin.copy.
+        type: str
+        required: false
+        default: ""
+      nextcloud__postgres_password:
+        description: The password to use for the nextcloud PostgreSQL user.
+        type: str
+        required: true
+      nextcloud__proxy_protocol_reverse_proxy_ip:
+        description: The IP of the reverse proxy to do proxy protocol with.
+        type: str
+        required: true
+      nextcloud__certbot_acme_account_email_address:
+        description: The E-Mail address to pass to certbot to use for the ACME account.
+        type: str
+        required: true