Merge pull request #20787 from fbuihuu/watchdog-more-rework

Watchdog more rework

diff --cc man/systemd-system.conf.xml
Simple merge

diff --cc src/core/load-fragment.c
Simple merge

diff --cc src/core/load-fragment.h
Simple merge

diff --cc src/core/main.c
Simple merge

diff --cc src/core/manager.c
Simple merge