r/frigate-exporter: Deploy Prometheus exporter

Frigate exports useful statistics natively, but in a custom JSON format.
There is a [feature request][0] to add support for Prometheus format,
but it's mostly being ignored.  A community member has created a
standalone process that converts the JSON format into Prometheus format,
though, which we can use.

[0]: https://github.com/blakeblackshear/frigate/issues/2266

roles/frigate-exporter/tasks/main.yml

@@ -0,0 +1,47 @@
+- name: ensure frigate-exporter container image is available
+  podman_image:
+    name: git.pyrocufflink.net/containerimages/prometheus-frigate-exporter:latest
+    state: present
+  environment:
+    http_proxy: '{{ http_proxy }}'
+    https_proxy: '{{ https_proxy }}'
+  tags:
+  - install
+  - container-image
+
+- name: ensure frigate-exporter container unit is defined
+  copy:
+    src: frigate-exporter.container
+    dest: /etc/containers/systemd/frigate-exporter.container
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  notify:
+  - reload systemd
+  - restart frigate-exporter
+  tags:
+  - container
+  - systemd
+
+- name: flush handlers
+  meta: flush_handlers
+
+- name: ensure frigate-exporter is running
+  service:
+    name: frigate-exporter
+    state: started
+  tags:
+  - service
+
+- name: ensure firewall is configured for frigate-exporter
+  firewalld:
+    port: 9100/tcp
+    immediate: '{{ item == "immediate" }}'
+    permanent: '{{ item == "permanent" }}'
+    state: enabled
+  loop:
+  - immediate
+  - permanent
+  when: host_uses_firewalld|d(true)
+  tags:
+  - firwalld