[Web support] Add `init` method to load JS SDK and create factory instance#157

EmilianoSanchez merged 1 commit intoFME-11223-web-support_baselinesplitio/flutter-sdk-plugin:FME-11223-web-support_baselinefrom

FME-11223-web-support-factory-singletonsplitio/flutter-sdk-plugin:FME-11223-web-support-factory-singletonCopy head branch name to clipboard