Log NSData as human readable string

Currently, I see messages being logged as:
```
registerToken failed:, Unable to find a push integration set up for application iOSStaging on APNS_SANDBOX, got response 126 bytes
```

This change should make them appear as:
```
registerToken failed:, Unable to find a push integration set up for application iOSStaging on APNS_SANDBOX, got response Optional("{\"msg\":\"Unable to find a push integration set up for application iOSStaging on APNS_SANDBOX\",\"code\":\"BadParams\",\"params\":null}")
```

Update swift-sdk/Internal/IterableAPIInternal.swift

Co-Authored-By: tapashmajumder <[email protected]>

Update swift-sdk/Internal/IterableAPIInternal.swift

Co-Authored-By: tapashmajumder <[email protected]>

Update swift-sdk/Internal/IterableAPIInternal.swift

Co-Authored-By: tapashmajumder <[email protected]>

Author: 2 people

swift-sdk/Internal/IterableAPIInternal.swift

@@ -606,7 +606,7 @@ final class IterableAPIInternal : NSObject, PushTrackerProtocol {
                 toLog += ", \(reason)"
             }
             if let data = data {
-                toLog += ", got response \(data)"
+                toLog += ", got response \(String(data: data, encoding: .utf8) ?? "nil")"
             }
             ITBError(toLog)
         }