[ pg_ctl ] Review Request for Adding Pre-check User Script Feature

Hello,

I have been considering adding a user script that performs pre-checks
before executing the start, stop, and restart operations in pg_ctl. I
believe it is necessary for pg_ctl to support an extension that can prevent
various issues that might occur when using start and stop. To this end, I
have sought a way for users to define and use their own logic. The existing
behavior remains unchanged, and the feature can be used optionally when
needed.

The verification of the code was carried out using the methods described
below, and I would like to request additional opinions or feedback. Tests
were conducted using make check and through direct testing under various
scenarios. As this is my first contribution, there might be aspects I
missed or incorrectly designed.

I would appreciate it if you could review this.

Thank you.

Myoungjun Kim / South Korea