log: introduce new helper call log_setup_service()

Let's reduce the common boilerplate and have a single setup function
used by all service code to setup logging.

src/basic/log.c

@@ -1337,3 +1337,13 @@ int log_dup_console(void) {
         console_fd = copy;
         return 0;
 }
+
+void log_setup_service(void) {
+        /* Sets up logging the way it is most appropriate for running a program as a service. Note that using this
+         * doesn't make the binary unsuitable for invocation on the command line, as log output will still go to the
+         * terminal if invoked interactively. */
+
+        log_set_target(LOG_TARGET_AUTO);
+        log_parse_environment();
+        log_open();
+}

src/basic/log.h

@@ -318,3 +318,5 @@ int log_syntax_invalid_utf8_internal(
         })
 
 #define DEBUG_LOGGING _unlikely_(log_get_max_level() >= LOG_DEBUG)
+
+void log_setup_service(void);