feat: allow users to bind to all interfaces when a proxy is enabled

- use a plugin trigger to see whether we should bind to all interfaces
- create a generic way of setting properties for a plugin
- migrate proxy-enabled to the new network property "bind-all-interfaces"
- add network:set subcommand

plugins/network/src/triggers/post-create/post-create.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"flag"
+
+	common "github.com/dokku/dokku/plugins/common"
+)
+
+// set bind-all-interfaces to false by default
+func main() {
+	flag.Parse()
+	appName := flag.Arg(0)
+
+	common.PropertyWrite("network", appName, "bind-all-interfaces", "false")
+}