[d8 advagg] new configuration for limiting IE selectors

[pricejn2]

https://github.com/omega8cc/boa/blob/ee91623337434a4757259e281a0dc36cc467006b/aegir/conf/global.inc#L824

This should be updated to the following per current advagg module standards for D8.

$config['advagg_old_ie_compatibility.settings']['active'] = true;