When an app has no web listeners (not yet deployed, no web process type,
or web processes not running), generate a minimal nginx config that
returns 502 Bad Gateway instead of having no config at all. This ensures
domains resolve, monitoring tools detect non-200 status codes, and SSL
certificate provisioning tools like letsencrypt can function.
While I do not agree with _every_ style change, this will force Dokku to have consistent formatting across all shell scripts, which is arguably a Good Thing™.
The command used to reprocess everything is:
```shell
shfmt -l -bn -ci -i 2 -w .
```
- Add proxy-build-config hook to rebuild network and proxy settings for an application
- Scope nginx:build-config to work only when it is the configured proxy for an application
- Refactor deploy code to interact with network plugin for computed and actual ipaddr/port settings
- Ensure the proxy-build-config plugin trigger is called on ps:restore
- Expose a few plugin triggers for retrieving networking information for a given APP/PROC_TYPE/CONTAINER_ID combination
