Define systemd entrypoint

[guidograzioli]

Refactor the systemd tasks file to allow executing as entrypoint (to add systemd control to already existing activemq deployments).

To execute:

- name: Install systemd unit for activemq service
  ansible.builtin.include_role:
    - name: activemq    
      tasks_from: systemd

Refer to argument specs for the systemd entrypoint to see the reduced parameter list.