Systemd timer not preserved across reboots

[k-ta-yamada]

roles/postgresql/templates/postgresql.logrotate.timer.j2

Add the following to the above file.

[Install]
WantedBy=timers.target

ref:

• Systemd timer not preserved across reboots : archlinux
  https://www.reddit.com/r/archlinux/comments/44ikfk/systemd_timer_not_preserved_across_reboots/
• Systemd timer not active after reboot : linuxquestions
  https://www.reddit.com/r/linuxquestions/comments/3n2wds/systemd_timer_not_active_after_reboot/