Add a Safari Pinned Tab Icon (#8983)

Icon adopted from grafana_icon.svg

Reference document:
https://developer.apple.com/library/content/documentation/AppleApplicati
ons/Reference/SafariWebContent/pinnedTabs/pinnedTabs.html

public/views/index.html

@@ -17,6 +17,7 @@
 		[[end]]
 
     <link rel="icon" type="image/png" href="[[.AppSubUrl]]/public/img/fav32.png">
+    <link rel="mask-icon" href="[[.AppSubUrl]]/public/grafana_mask_icon.svg" color="#F05A28">
 		<base href="[[.AppSubUrl]]/" />
 
 	</head>