List available projects in a workspace - `ng projects`

# 🚀 Feature request

### Command (mark with an `x`)

- [X] projects

### Description

In large Angular monorepo workspaces, it can sometimes be non-obvious to discover all the available projects which can be built. We should consider a new command (`ng projects`, `ng ls`, etc.) which lists all the projects in the current workspace. This can help new developers in workspace figure out exactly what they want to work on and how to do it.

### Describe alternatives you've considered

Workaround is to introspect the `angular.json` file, which is not obvious or easy to do, especially for a new developer.

Comienza examinando cómo Angular CLI lee el angular.json del espacio de trabajo actual y cómo se registran los comandos existentes. Compara los puntos de entrada propuestos `ng projects` y `ng ls` y, a continuación, verifica que el comando elegido enumere todos los proyectos disponibles del espacio de trabajo y explique cómo se puede usar cada uno.

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