Merge pull request #20813 from unusual-thoughts/exittype_v2

Reintroduce ExitType

diff --cc docs/TRANSIENT-SETTINGS.md
Simple merge

diff --cc man/org.freedesktop.systemd1.xml
Simple merge

diff --cc src/core/load-fragment-gperf.gperf.in
Simple merge

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

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

diff --cc src/shared/bus-unit-util.c
Simple merge

diff --cc test/fuzz/fuzz-unit-file/directives.service
Simple merge