unifi: Deploy Unifi Network controller

Since Ubiquiti only publishes Debian packages for the Unifi Network
controller software, running it on Fedora has historically been neigh
impossible.  Fortunately, a modern solution is available: containers.
The *linuxserver.io* project publishes a container image for the
controller software, making it fairly easy to deploy on any host with an
OCI runtime.  I briefly considered creating my own image, since theirs
must be run as root, but I decided the maintenance burden would not be
worth it.  Using Podman's user namespace functionality, I was able to
work around this requirement anyway.

roles/unifi/tasks/install.yml

@@ -0,0 +1,12 @@
+- name: ensure podman is installed
+  dnf:
+    name:
+    - container-selinux
+    - podman
+    install_weak_deps: false
+    state: present
+
+- name: ensure unifi container image is present
+  podman_image:
+    name: '{{ unifi_container_image }}:{{ unifi_version }}'
+    state: present