V12: Map |DataDirectory| to path in connectionString (#14278)

* Add Data directory as constants

* Use new constants instead of internal ones

* Replace data directory in connection string if its there

* Update src/Umbraco.Cms.Persistence.EFCore/Extensions/UmbracoEFCoreServiceCollectionExtensions.cs

---------

Co-authored-by: Zeegaan <nge@umbraco.dk>
Co-authored-by: Mole <nikolajlauridsen@protonmail.ch>

src/Umbraco.Core/Constants-System.cs

@@ -64,5 +64,15 @@ public static partial class Constants
 
         public const string UmbracoConnectionName = "umbracoDbDSN";
         public const string DefaultUmbracoPath = "~/umbraco";
+
+        /// <summary>
+        /// The DataDirectory name.
+        /// </summary>
+        public const string DataDirectoryName = "DataDirectory";
+
+        /// <summary>
+        /// The DataDirectory placeholder.
+        /// </summary>
+        public const string DataDirectoryPlaceholder = "|DataDirectory|";
     }
 }