chore: clean up "contrib" dir (#37690)

1. remove useless files like "backport.go", "update_dependencies.sh"
2. remove outdated "init" scripts, only keep one in sysvinit, gentoo dir
is also kept because it still uses openrc
3. move "service" related config and scripts into "service" directory

contrib/service/openwrt/gitea

@@ -0,0 +1,35 @@
+#!/bin/sh /etc/rc.common
+
+USE_PROCD=1
+
+# PROCD_DEBUG=1
+
+START=90
+STOP=10
+
+PROG=/opt/gitea/gitea
+GITEA_WORK_DIR=/opt/gitea
+CONF_FILE=$GITEA_WORK_DIR/app.ini
+
+start_service(){
+    procd_open_instance gitea
+    procd_set_param env GITEA_WORK_DIR=$GITEA_WORK_DIR
+    procd_set_param env HOME=$GITEA_WORK_DIR
+    procd_set_param command $PROG web -c $CONF_FILE
+    procd_set_param file $CONF_FILE
+    procd_set_param user git
+    procd_set_param respawn ${respawn_threshold:-3600} ${respawn_timeout:-5} ${respawn_retry:-5} # respawn automatically if something died, be careful if you have an alternative process supervisor
+    procd_close_instance
+}
+
+start(){
+    service_start $PROG
+}
+
+stop(){
+    service_stop $PROG
+}
+
+reload(){
+    service_reload $PROG
+}