loki: Add role+playbook for Grafana Loki

The current Grafana Loki server, *loki0.pyrocufflink.blue*, runs Fedora
CoreOS and is managed by Ignition and *cfg*.  Since I have declared
*cfg* a failed experiment, I'm going to re-deploy Loki on a new VM
running Fedora Linux and managed by Ansible.

The *loki* role installs Podman and defines a systemd-managed container
to run Grafana Loki.

roles/loki/tasks/main.yml

@@ -0,0 +1,67 @@
+- name: ensure required packages are installed
+  package:
+    name:
+    - podman
+    state: present
+  tags:
+  - install
+
+- name: ensure loki container unit is configured
+  copy:
+    src: loki.container
+    dest: /etc/containers/systemd/loki.container
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  notify:
+  - reload systemd
+  tags:
+  - container
+
+- name: ensure loki configuration directory exists
+  file:
+    path: /etc/loki
+    owner: root
+    group: root
+    state: directory
+  tags:
+  - config
+- name: ensure loki is configured
+  copy:
+    dest: /etc/loki/config.yml
+    content: >-
+      {{ loki_config|to_nice_yaml(indent=2) }}
+    owner: root
+    group: root
+    mode: u=rw,go=r
+  tags:
+  - config
+
+- name: flush handlers
+  meta: flush_handlers
+
+- name: ensure loki starts at boot
+  service:
+    name: loki
+    enabled: true
+  tags:
+  - service
+- name: ensure loki is running
+  service:
+    name: loki
+    state: started
+  tags:
+  - service
+
+- name: ensure firewall is configured for loki
+  firewalld:
+    port: '{{ item }}'
+    state: enabled
+    immediate: true
+    permanent: true
+  loop:
+  - 3100/tcp
+  - 9096/tcp
+  when: host_uses_firewalld|d(true)|bool
+  tags:
+  - firewalld