Modify OSRequestGetInAppMessages method to include new header values

Motivation: we need to pass the offset, session duration, & retry count to the GET IAM request.

iOS_SDK/OneSignalSDK/OneSignalInAppMessages/Requests/OSInAppMessagingRequests.h

@@ -29,7 +29,7 @@
 #import "OSInAppMessageClickResult.h"
 
 @interface OSRequestGetInAppMessages : OneSignalRequest
-+ (instancetype _Nonnull)withSubscriptionId:(NSString * _Nonnull)subscriptionId;
++ (instancetype _Nonnull)withSubscriptionId:(NSString * _Nonnull)subscriptionId withSessionDuration:(NSNumber * _Nonnull)sessionDuration withRetryCount:(NSNumber *)retryCount withRywToken:(NSString *)rywToken;
 @end
 
 @interface OSRequestInAppMessageViewed : OneSignalRequest

iOS_SDK/OneSignalSDK/OneSignalInAppMessages/Requests/OSInAppMessagingRequests.m

@@ -28,9 +28,25 @@ of this software and associated documentation files (the "Software"), to deal
 #import "OSInAppMessagingRequests.h"
 
 @implementation OSRequestGetInAppMessages
-+ (instancetype _Nonnull)withSubscriptionId:(NSString * _Nonnull)subscriptionId {
++ (instancetype _Nonnull)   withSubscriptionId:(NSString * _Nonnull)subscriptionId
+                            withSessionDuration:(NSNumber * _Nonnull)sessionDuration
+                            withRetryCount:(NSNumber *)retryCount
+                            withRywToken:(NSString *)rywToken
+{
     let request = [OSRequestGetInAppMessages new];
     request.method = GET;
+    let headers = [NSMutableDictionary new];
+
+    if (sessionDuration != nil) {
+        // convert to ms & round
+        sessionDuration = @(round([sessionDuration doubleValue] * 1000));
+        headers[@"OneSignal-Session-Duration" ] = [sessionDuration stringValue];
+    }
+    headers[@"OneSignal-RYW-Token"] = rywToken;
+    headers[@"OneSignal-Retry-Count"] = [retryCount stringValue];
+
+    request.additionalHeaders = headers;
+
     NSString *appId = [OneSignalConfigManager getAppId];
     request.path = [NSString stringWithFormat:@"apps/%@/subscriptions/%@/iams", appId, subscriptionId];
     return request;