Make user directive optional

[fuero]

The default for the user directive in pgBouncer is "not present".
Using it creates problems running this container in Kubernetes/OpenShift with securityContexts given.
Making it optional allows using a UID that's not postgres or root.

Also, I filtered the entrypoint script through shellcheck, applied autofixes, and manually applied the POSIX compatibility recommendations.

[jflambert]

Thanks for the contribution @fuero

For my information, can you point out where user is optional under [pgbouncer]? In fact I seem unable to find documentation on that particular config item.

At this point my preferred approach would be to maintain postgres as a default value, unless disabled or overridden, out of concern for existing deployments.

[fuero]

In the link you mentioned under the text for the user directive it says Default: not set
Which to me says "optional"

[jflambert]

In the link you mentioned under the text for the user directive it says Default: not set Which to me says "optional"

Thanks, it's right at the top under "Generic settings"

I'm still worried about previously imposing postgres and suddenly switching to unset.