Add environment variables for PHP error display and logging

[shankie-codes]

I've just run into an issue on a prod server where, upon investigation, it turns out that PHP's display_errors is turned on by default in this image.

I've suppressed it by adding echo "display_errors=0" >> /usr/local/etc/php/conf.d/errors.ini to my Dockerfile (that's FROM this one), but it would be nice if this was handled out of the box.

I'm happy to do a PR for this, but I just wondered whether there was any reason why you had decided not to do this.

[tianon]

Sorry for the massive delay!

The reason we didn't do that is that we've left almost all the settings either at their upstream-supplied defaults, or at the upstream-recommended values. If there's a recommendation from upstream to disable display_errors by default, it would make sense to do, but otherwise we likely won't.