Add CAP_PERFMON to AmbientCapabilities in capabilities.conf, to enable
perf_event based stall detector in Seastar.
However, on Debian/Ubuntu CAP_PERFMON with non-root user does not work
because it sets kernel.perf_event_paranoid=4 which disallow all non-root
user access.
(On Debian it kernel.perf_event_paranoid=3)
So we need to configure kernel.perf_event_paranoid=2 on these distros.
see: https://askubuntu.com/questions/1400874/what-does-perf-paranoia-level-four-do
Also, CAP_PERFMON is only available on linux-5.8+, older kernel does not
have this capability.
To enable older kernel environment such as CentOS7, we need to configure
kernel.perf_event_paranoid=1 to allow non-root user access even without
the capability.
Fixes#15743Closesscylladb/scylladb#16070
f90c10260f