docs: Improve examples of Interceptors with more implementation details

In https://loopback.io/doc/en/lb4/Interceptors.html#example-interceptors
there are different examples of interceptors.

To understand the example implementations of these interceptors, let's
also show an example implementation of what they are intercepting.

For example:

/**
 * A binding provider class to produce an interceptor that validates the
 * `name` argument
 */
class NameValidator implements Provider<Interceptor> {
  constructor(@inject('valid-names') private validNames: string[]) {}

  value() {
    return this.intercept.bind(this);
  }

  // (doc improvement)
  // This interceptor works as an authorizer for certain endpoints,
  // which takes in the first argument as the name.
  async intercept<T>(
    invocationCtx: InvocationContext,
    next: () => ValueOrPromise<T>,
  ) {
    const name = invocationCtx.args[0];
    if (!this.validNames.includes(name)) {
      throw new Error(
        `Name '${name}' is not on the list of '${this.validNames}`,
      );
    }
    return next();
  }
}

It is not clear what this interceptor is attached to. Is it a function, a class, a request?

How do we know that the name we need to validate is in args[0] of the invocation context?

Providing more implementation details would shed some light on how to use them.

See Reporting Issues for more tips on writing good issues

Acceptane Criteria

• Refine the docs to include more details described above.
• For the example snippet, it implies we need to add more details to InvocationContext's properties, like args, see https://loopback.io/doc/en/lb4/apidocs.context.invocationcontext.html#properties

Comienza con la documentación de Interceptors en el ejemplo enlazado y revisa las propiedades enlazadas de la API InvocationContext, especialmente args. Aclara a qué está asociado el interceptor, cómo los argumentos del método interceptado se asignan a args[0], y añade los detalles de implementación solicitados; los criterios de aceptación deben cumplirse cuando el ejemplo sea comprensible sin estas preguntas sin respuesta.