run: allow setting output format

This is useful when moving from `--pty` or `--pipe` to using
`--verbose`: you can use `--verbose-output=cat` to get similar output on
stdout while still having all of the advantages of `--verbose` over the
other options.

src/shared/fork-notify.c

@@ -205,7 +205,7 @@ void fork_notify_terminate_many(sd_event_source **array, size_t n) {
         free(array);
 }
 
-int journal_fork(RuntimeScope scope, char * const* units, PidRef *ret_pidref) {
+int journal_fork(RuntimeScope scope, char * const* units, OutputMode output, PidRef *ret_pidref) {
         assert(scope >= 0);
         assert(scope < _RUNTIME_SCOPE_MAX);
 
@@ -228,5 +228,9 @@ int journal_fork(RuntimeScope scope, char * const* units, PidRef *ret_pidref) {
                                  *u) < 0)
                         return log_oom_debug();
 
+        if (output >= 0)
+                if (strv_extendf(&argv, "--output=%s", output_mode_to_string(output)) < 0)
+                        return log_oom_debug();
+
         return fork_notify(argv, ret_pidref);
 }