[CM-1798] Event Trigger via message meta data bug

[AbhijeetRanjan308]

Summary

• Fixed Message Metadata typeCasting in iOS Side.
• Need to pass the data in object format

Code

dynamic metadataObject = {'CUSTOM_WELCOME_EVENT' : 'welcome_sti'};
dynamic conversationObject = {'appId': <YOUR-APP-ID>, 'messageMetadata': metadataObject}; 
/// user can pass this conversation object in Build conversation function