Add ext_ubol directive

Originally proposed in https://github.com/AdguardTeam/CoreLibs/issues/1966 but it seems it should be done here. Please consider to add `ext_ubol` for uBlock Origin Lite which occaisonally needs different filters than uBlock Origin. And a question, is it feasible to create dedicated lists for uBOL like `https://filters.adtidy.org/extension/ubol/filters/2.txt` ? If it's no problem at all, maybe `ext_ubol` should be totally independent from `ext_ublock`. If it costs in any way, maybe `ext_ubol` should be a sub-catogory of `ext_ublock` and `ext_ubol` should be left in the distributed filters, so the current filter lists for uBO will be used for uBOL too and then uBO/uBOL chooses to use proper filter rules by looking the directive.