Enhance types generation

**Is your feature request related to a problem? Please describe.**

Currently, all types are optional, or at least a lot of them. See: https://github.com/search?q=repo:googleapis/google-api-nodejs-client+%22%7C+null%22&type=code So, this leads to an awful development experience.

For example, see Google Calendar API:

https://github.com/googleapis/google-api-nodejs-client/blob/6e8c998cee93dbc79a6f306c2150414b933c22c9/src/apis/calendar/v3.ts#L720

But on the other hand, we can see in docs that some fields are optional and some are not.

https://developers.google.com/calendar/api/v3/reference/events#resource


**Describe the solution you'd like**
I would like to see real types with the minimum amount of optional fields.

**Describe alternatives you've considered**
Of course, we can check everything manually or disable TypeScript checking at all. But I believe it's not a good solution, as why do we need typings which do not work.
https://github.com/googleapis/google-api-nodejs-client/issues/3151

Inizia con il tipo generato in src/apis/calendar/v3.ts nella sezione relativa all'esempio collegato di Calendar API, quindi confronta i suoi campi facoltativi con la documentazione delle risorse di Google Calendar e con l'issue #3151. Il lavoro sarà completato quando il generatore di tipi produrrà campi obbligatori laddove la documentazione dell'API li identifica come obbligatori, senza rendere facoltativi tutti i campi indiscriminatamente.

Scritto dal modello di indicizzazione a partire dal testo della issue.