manager: add 'needs-stop/needs-start' markers

Useful for packaging scripts, when units are removed.
When multiple markers are assigned without +/-, the last one wins.
When using +/-, the job merging logic is followed to the extent possible.

src/basic/unit-def.c

@@ -155,6 +155,8 @@ FreezerState freezer_state_objective(FreezerState state) {
 static const char* const unit_marker_table[_UNIT_MARKER_MAX] = {
         [UNIT_MARKER_NEEDS_RELOAD]  = "needs-reload",
         [UNIT_MARKER_NEEDS_RESTART] = "needs-restart",
+        [UNIT_MARKER_NEEDS_STOP]    = "needs-stop",
+        [UNIT_MARKER_NEEDS_START]   = "needs-start",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(unit_marker, UnitMarker);