Add manual tests and test scenario for BZ-1894149

[shubhamsg199]

Test Results:

$ pytest -v --ansible-host-pattern server --ansible-user=root  --ansible-inventory testfm/inventory tests/test_health.py -k test_positive_check_postgresql_checkpoint_segments
=============================================== test session starts =====================================================
platform linux -- Python 3.8.6, pytest-3.6.1, py-1.10.0, pluggy-0.6.0 -- /home/sganar/foreman/fm/bin/python
cachedir: .pytest_cache
ansible: 2.9.20
rootdir: /home/sganar/foreman/testfm, inifile:
plugins: ansible-2.2.3
collected 29 items / 28 deselected                                                                                                                                                                                

tests/test_health.py::test_positive_check_postgresql_checkpoint_segments PASSED                                                                                                                             [100%]

====================================== 1 passed, 28 deselected in 90.76 seconds ===============================================