Add ext_ubol directive

[Yuki2718]

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.