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/promtail.yml.j2

@@ -4,7 +4,7 @@ server:
   grpc_listen_port: 0
 
 positions:
-  filename: /var/lib/grafana-promtail/positions.yaml
+  filename: /var/lib/promtail/positions.yaml
 
 clients:
 {% for i in prometheus_agent.scrapers if prometheus_agent.scrapers[i].get("loki") %}