feat(iOS WkWebview): Add applicationNameForUserAgent support (#506)

docs/Reference.md

 - [`mixedContentMode`](Reference.md#mixedcontentmode)
 - [`thirdPartyCookiesEnabled`](Reference.md#thirdpartycookiesenabled)
 - [`userAgent`](Reference.md#useragent)
+- [`applicationNameForUserAgent`](Reference.md#applicationNameForUserAgent)
 - [`allowsFullscreenVideo`](Reference.md#allowsfullscreenvideo)
 - [`allowsInlineMediaPlayback`](Reference.md#allowsinlinemediaplayback)
 - [`bounces`](Reference.md#bounces)
 
 ---
 
+### `applicationNameForUserAgent`
+
+Append to the existing user-agent. Available on iOS WKWebView only. Setting `userAgent` will override this.
+
+| Type   | Required | Platform      |
+| ------ | -------- | ------------- |
+| string | No       | iOS WKWebView |
+
 ### `allowsFullscreenVideo`
 
 Boolean that determines whether videos are allowed to be played in fullscreen. The default value is `false`.

ios/RNCWKWebView.h

 @property (nonatomic, assign) BOOL incognito;
 @property (nonatomic, assign) BOOL useSharedProcessPool;
 @property (nonatomic, copy) NSString *userAgent;
+@property (nonatomic, copy) NSString *applicationNameForUserAgent;
 @property (nonatomic, assign) BOOL cacheEnabled;
 @property (nonatomic, assign) BOOL allowsLinkPreview;
 @property (nonatomic, assign) BOOL showsHorizontalScrollIndicator;

ios/RNCWKWebView.m

     wkWebViewConfig.mediaPlaybackRequiresUserAction = _mediaPlaybackRequiresUserAction;
 #endif
 
+    if (_applicationNameForUserAgent) {
+        wkWebViewConfig.applicationNameForUserAgent = [NSString stringWithFormat:@"%@ %@", wkWebViewConfig.applicationNameForUserAgent, _applicationNameForUserAgent];
+    }
+
     if(_sharedCookiesEnabled) {
       // More info to sending cookies with WKWebView
       // https://stackoverflow.com/questions/26573137/can-i-set-the-cookies-to-be-used-by-a-wkwebview/26577303#26577303

ios/RNCWKWebViewManager.m

 RCT_EXPORT_VIEW_PROPERTY(incognito, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(pagingEnabled, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(userAgent, NSString)
+RCT_EXPORT_VIEW_PROPERTY(applicationNameForUserAgent, NSString)
 RCT_EXPORT_VIEW_PROPERTY(cacheEnabled, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(allowsLinkPreview, BOOL)