Remove compatibility with Ubuntu 18.04

[vitabaks]

The repository https://apt.postgresql.org/pub/repos/apt bionic-pgdg does not have a Release file.

  TASK [add-repository : Add repository apt-key] *********************************
  changed: [10.172.0.21] => (item={'key': 'https://www.postgresql.org/media/keys/ACCC4CF8.asc'})
  changed: [10.172.0.22] => (item={'key': 'https://www.postgresql.org/media/keys/ACCC4CF8.asc'})
  changed: [10.172.0.20] => (item={'key': 'https://www.postgresql.org/media/keys/ACCC4CF8.asc'})
  failed: [10.172.0.21] (item={'repo': 'deb https://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main'}) => {"ansible_loop_var": "item", "changed": false, "item": {"repo": "deb https://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main"}, "msg": "Failed to update apt cache: E:The repository 'https://apt.postgresql.org/pub/repos/apt bionic-pgdg Release' does not have a Release file."}
  failed: [10.172.0.20] (item={'repo': 'deb https://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main'}) => {"ansible_loop_var": "item", "changed": false, "item": {"repo": "deb https://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main"}, "msg": "Failed to update apt cache: E:The repository 'https://apt.postgresql.org/pub/repos/apt bionic-pgdg Release' does not have a Release file."}
  failed: [10.172.0.22] (item={'repo': 'deb https://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main'}) => {"ansible_loop_var": "item", "changed": false, "item": {"repo": "deb https://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main"}, "msg": "Failed to update apt cache: E:The repository 'https://apt.postgresql.org/pub/repos/apt bionic-pgdg Release' does not have a Release file."}
  
  TASK [add-repository : Add repository] *****************************************