'Parallel Safety' in CBDB style parallel plan

### Cloudberry Database version

_No response_

### What happened

According to https://www.postgresql.org/docs/14/parallel-safety.html
> The planner classifies operations involved in a query as either parallel safe, parallel restricted, or parallel unsafe. A parallel safe operation is one that does not conflict with the use of parallel query. A parallel restricted operation is one that cannot be performed in a parallel worker, but that can be performed in the leader while parallel query is in use.

However, in our CBDB style parallel, there is no leader process at all.
The `parallel restricted` concept should be reconsidered.

### What you think should happen instead

_No response_

### How to reproduce

NA

### Operating System

NA

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes, I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://cloudberrydb.org/community/coc).

Inizia leggendo la documentazione di PostgreSQL 14 sulla sicurezza parallela e confrontando le sue assunzioni su leader/worker con l'esecuzione parallela in stile CBDB descritta qui. Per considerare il lavoro completato, è necessario decidere come trattare il concetto parallel-restricted e apportare una modifica corrispondente, documentata o implementata, ma questo issue non indica file né test.

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