fix: export AttachmentSelectorContext from the SDK (#3158)

(cherry picked from commit 68efeb5)

Author: MartinCupela

src/context/index.ts

@@ -1,3 +1,4 @@
+export * from './AttachmentSelectorContext';
 export * from './ChannelActionContext';
 export * from './ChannelListContext';
 export * from './ChannelStateContext';