enable iCloud Drive for attachments

deltachat-ios/deltachat-ios.entitlements

@@ -6,6 +6,10 @@
 	<string>development</string>
 	<key>com.apple.developer.associated-domains</key>
 	<array/>
+	<key>com.apple.developer.icloud-container-identifiers</key>
+	<array/>
+	<key>com.apple.developer.ubiquity-kvstore-identifier</key>
+	<string>$(TeamIdentifierPrefix)$(CFBundleIdentifier)</string>
 	<key>com.apple.security.application-groups</key>
 	<array>
 		<string>group.eu.merlinux.group.chat.delta.ios</string>