Use Grafana's upstream Debian packages for promtail

Migration playbook:

- name: Cleanup old promtail install
  hosts: all
  tasks:
  - name: Stop and disable old service
    when: prometheus_agent.agents.promtail.enable
    service:
      name: grafana-promtail
      state: stopped
      enabled: false
  - name: Migrate state dir
    when: prometheus_agent.agents.promtail.enable
    copy:
      src: /var/lib/grafana-promtail/
      dest: /var/lib/promtail/
      remote_src: yes
  - name: Uninstall old package
    when: prometheus_agent.agents.promtail.enable
    apt:
      name: grafana-promtail
      state: absent
      purge: true # Removes user, group and /var/lib/grafana-promtail
  - name: create promtail group
    when: prometheus_agent.agents.promtail.enable
    group:
      name: promtail
      system: true
  - name: create promtail user
    when: prometheus_agent.agents.promtail.enable
    user:
      name: promtail
      system: true
      group: promtail
      home: /var/lib/promtail
  - name: Fix state dir owner and group
    when: prometheus_agent.agents.promtail.enable
    file:
      name: /var/lib/promtail/
      state: directory
      recurse: true
      owner: promtail
      group: promtail

templates/grafana-promtail.yml.j2

@@ -1,44 +0,0 @@
-server:
-  disable: true
-  http_listen_port: 9080
-  grpc_listen_port: 0
-
-positions:
-  filename: /var/lib/grafana-promtail/positions.yaml
-
-clients:
-{% for i in prometheus_agent.scrapers if prometheus_agent.scrapers[i].get("loki") %}
-{% set lokiconfig = {}|combine({ "external_labels": merged_prometheus_labels|combine( {"instance": inventory_hostname} ) }, prometheus_agent.scrapers[i]['loki'] ) %}
-  - {{ lokiconfig|to_json }}
-{% endfor %}
-
-scrape_configs:
-- job_name: system
-  static_configs:
-  - targets:
-      - localhost
-    labels:
-      job: varlogs
-      __path__: /var/log/*log
-- job_name: journal
-  journal:
-    max_age: 12h
-    labels:
-      job: systemd-journal
-  relabel_configs:
-    - source_labels: ['__journal__systemd_unit']
-      target_label: 'unit'
-- job_name: nginx
-  static_configs:
-  - targets:
-      - localhost
-    labels:
-      job: nginx
-      __path__: /var/log/nginx/access-promtail.log
-- job_name: postfix-bounces
-  static_configs:
-  - targets:
-      - localhost
-    labels:
-      job: postfix-bounces
-      __path__: /var/log/mailman3/bounce.log