Add a check for upgrader_process_complete

## What problem would the enhancement address for VIP?

Because the contents of `/wp-content/plugins` and `/wp-content/themes` are setup as `read-only` directories, and end-users can't install or update plugins from within the `wp-admin`, the [hook `upgrader_process_complete`](https://developer.wordpress.org/reference/hooks/upgrader_process_complete/) will never run for either plugin install or update on the VIP Go platform.

When a VIP customer installs a plugin (via the [GitHub repo](https://docs.wpvip.com/technical-references/vip-codebase/)) with a function tied to that hook, their development team has to reverse engineer the plugin's code to execute that functionality.

This is not entirely unique to VIP, but only impacts WordPress environments where the `/wp-content/plugins` and `/wp-content/themes` are `read-only`, so it may not be a good fit for the [WordPress Coding Standards](https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards/).

## Describe the solution you'd like

A sniff that will flag places where the [`upgrader_process_complete` hook](https://developer.wordpress.org/reference/hooks/upgrader_process_complete/) is used. Preferably as an error because it is functionality that will not work.

## What code should be reported as a violation?

```
add_action( 'upgrader_process_complete', 'my_upgrade_function',10, 2);
```

## What code should *not* be reported as a violation?

I'm unaware of cases where this might be detected as a false positive.

## Additional context

_None applicable_

Empieza leyendo las convenciones existentes de sniff y pruebas del repositorio, y después sigue cómo se detectan las llamadas al hook de WordPress upgrader_process_complete. El issue proporciona el hook objetivo y un ejemplo de add_action que infringe la regla; el trabajo está terminado cuando el sniff informa de ese uso como un error sin que se haya identificado ningún caso de falso positivo.

Escrito por el modelo de indexación a partir del texto del issue.