postgres: Fix incorrect shebang in example initialization script

[reidb1]

The /bin/bash shebang points does not point to the correct path for bash in the container. Because of this, the initialization scripts will not run. Changing to /usr/bin/env bash fixes this problem.

Alternatively /usr/bin/bash would also work.

[tianon]

Thanks! This is fine, although I'll note that all the images we maintain/support do have a valid /bin/bash, even if it's under a symlink. 🤔

[reidb1]

Interesting... I ran init scripts with #!/bin/bash and they did not run. ONLY change I made was #!/usr/bin/env bash and they ran...

Maybe there was something else that changed, but I was trying to be careful to make single changes at a time.