feat: use ports-clear plugn trigger to manage clearing the port map

This removes any access to the underlying implementation for port map clearing, which will make it easier to refactor the actual clearing.

docs/development/plugin-triggers.md

@@ -1242,12 +1242,32 @@ nginx -t
 ```
 
 ### `ports-get`
+
 - Description: Returns a list of port mappings, newline delimited
 - Invoked by: Various networking plugins
 - Arguments `$APP`
+- Example:
+
 ```shell
 #!/usr/bin/env bash
+
 set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+
+# TODO
+```
+
+### `ports-clear`
+
+- Description: Clears the ports for a given app without triggering further restarts or rebuilds
+- Invoked by: internally
+- Arguments: `$APP`
+- Example:
+
+```shell
+#!/usr/bin/env bash
+
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+
 # TODO
 ```