[Feature]: support `allow_alter_system` from PostgreSQL 17

[gbartolini]

Is there an existing issue already for this feature request/idea?

• [X] I have searched for an existing issue, and could not find anything. I believe this is a new feature request to be evaluated.

What problem is this feature going to solve? Why should it be added?

PostgreSQL 17 introduces support for the allow_alter_system option, with contributions from myself and Jelte Fennemia-Nio.

This is a cleaner and more robust way to disable the alter system command in CloudNativePG, currently implemented through #2725 .

Describe the solution you'd like

We should extend the existing implementation to use the native allow_alter_system configuration by default and keep the existing behaviour for PostgreSQL < 17.

For more information: https://www.postgresql.org/docs/devel/runtime-config-compatible.html#GUC-ALLOW-ALTER-SYSTEM

Describe alternatives you've considered

The best way is contained in the actual development thread in pgsql-hackers.

Additional context

No response

Backport?

Yes

Are you willing to actively contribute to this feature?

Yes

Code of Conduct

• [X] I agree to follow this project's Code of Conduct