[Feature]: enable PDB for pgbouncer with n+1 instances

### 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?

The operator does not deploy any PDB for pgbouncer deployments with n+1 replicas.

### Describe the solution you'd like

Deploy PDB to enforce minAvailable 1

### Describe alternatives you've considered

None

### 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