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

docs/networking/network.md

@@ -1,10 +1,11 @@
 # Network Management
 
-> New as of 0.10.0
+> New as of 0.11.0
 
 ```
 network:rebuild <app>                    # Rebuilds network settings for an app
 network:rebuildall                       # Rebuild network settings for all apps
+network:set <app> <key> (<value>)        # Set or clear a network property for an app
 ```
 
 The Network plugin allows developers to abstract the concept of container network management, allowing developers to both change what networks a given container is attached to as well as rebuild the configuration on the fly.
@@ -30,3 +31,55 @@ dokku network:rebuildall
 ```
 
 > This command will exit a non-zero number that depends on the number of containers for which configuration could not be built
+
+### Container network interface binding
+
+> This functionality does not control the `--network` docker flag. Please use the [docker-options plugin](docs/advanced-usage/docker-options.md) to manage this flag.
+
+By default, an application will only bind to the internal interface. This behavior can be modified per app by changing the `bind-all-interfaces` network property.
+
+```shell
+# bind to the default docker interface (`docker0`) with a random internal ip
+# this is the default behavior
+dokku network:set node-js-app bind-all-interfaces false
+
+# bind to all interfaces (`0.0.0.0`) on a random port for each upstream port
+# this will make the app container directly accessible by other hosts on your network
+# ports are randomized for every deploy, e.g. `0.0.0.0:32771->5000/tcp`.
+dokku network:set node-js-app bind-all-interfaces true
+```
+
+By way of example, in the default case, each container is bound to the docker interface:
+
+```shell
+docker ps
+```
+
+```
+CONTAINER ID        IMAGE                      COMMAND                CREATED              STATUS              PORTS               NAMES
+1b88d8aec3d1        dokku/node-js-app:latest   "/bin/bash -c '/star   About a minute ago   Up About a minute                       node-js-app.web.1
+```
+
+As such, the container's IP address will be an internal IP, and thus it is only accessible on the host itself:
+
+```
+docker inspect --format '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' node-js-app.web.1
+```
+
+```
+172.17.0.6
+```
+
+However, you can disable the internal proxying via the `network:set` command so that it will listen on the host's IP address:
+
+```shell
+dokku network:set node-js-app bind-all-interfaces true
+
+# container bound to all interfaces
+docker ps
+```
+
+```
+CONTAINER ID        IMAGE                      COMMAND                CREATED              STATUS              PORTS                     NAMES
+d6499edb0edb        dokku/node-js-app:latest   "/bin/bash -c '/star   About a minute ago   Up About a minute   0.0.0.0:49153->5000/tcp   node-js-app.web.1
+```