core: implement per unit journal rate limiting

Add LogRateLimitIntervalSec= and LogRateLimitBurst= options for
services. If provided, these values get passed to the journald
client context, and those values are used in the rate limiting
function in the journal over the the journald.conf values.

Part of #10230

src/shared/bus-unit-util.c

@@ -800,6 +800,14 @@ static int bus_append_execute_property(sd_bus_message *m, const char *field, con
 
                 return bus_append_parse_nsec(m, field, eq);
 
+        if (STR_IN_SET(field, "LogRateLimitIntervalSec"))
+
+                return bus_append_parse_sec_rename(m, field, eq);
+
+        if (streq(field, "LogRateLimitBurst"))
+
+                return bus_append_safe_atou(m, field, eq);
+
         if (streq(field, "MountFlags"))
 
                 return bus_append_mount_propagation_flags_from_string(m, field, eq);