For pg tables, allow users to skip auto-bounds detection

[nyurik]

Auto-bounds detection could be a relatively slow process. We may want to introduce some way to skip it.

martin --ignore-bounds postgres://...

In config, we have the option of specifying the bounds, but we don't want to force users to always supply them as [-180.0, -90.0, 180.0, 90.0]. Instead, we may want to allow max keyword.

Skipping bounds param in a config would always cause auto-detection. We may want to add another connection-wide config parameter to skip detection.

[nyurik]

added in #546