qa/standalone/mon/availability.sh: add test for config option

qa/standalone/mon/availability.sh: add test for config option

This commit adds two tests, first, to ensure we get an error
message when the feature is disabled. It checks if the config
option, enable_availability_tracking is working properly.
Second test ensures that we actually do stop calculating the
score when the feature is disabled.

Fixes: https://tracker.ceph.com/issues/71494
Signed-off-by: Shraddha Agrawal <shraddhaag@ibm.com>
(cherry picked from commit dc9ee94a8dc787324b898822fdaebfb83dfc7e37)