[feature/applySingle] implement apply for single
[feature/applySingle] implement apply for single

RxSwiftCommunity/RxSwiftExt,RxSwiftCommunity/RxSwiftExt,RxSwiftCommunity/RxSwiftExt,RxSwiftCommunity/RxSwift-Ext,RxSwiftCommunity/RxSwift-Ext