Update media picker migrators

Author: ronaldbarendse

src/Umbraco.Deploy.Contrib/Migrators/Legacy/DataType/MediaPicker2DataTypeArtifactMigrator.cs

@@ -13,7 +13,7 @@ public class MediaPicker2DataTypeArtifactMigrator : MediaPickerReplaceDataTypeAr
         private const string FromEditorAlias = "Umbraco.MediaPicker2";
 
         /// <inheritdoc />
-        protected override bool Multiple => true;
+        protected override bool Multiple => false;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="MediaPicker2DataTypeArtifactMigrator" /> class.

src/Umbraco.Deploy.Contrib/Migrators/Legacy/DataType/MediaPickerReplaceDataTypeArtifactMigratorBase.cs

@@ -32,7 +32,10 @@ protected MediaPickerReplaceDataTypeArtifactMigratorBase(string fromEditorAlias,
         /// <inheritdoc />
         protected override IDictionary<string, object> MigrateConfiguration(IDictionary<string, object> configuration)
         {
-            configuration["multiPicker"] = Multiple;
+            if (!configuration.ContainsKey("multiPicker"))
+            {
+                configuration["multiPicker"] = Multiple;
+            }
 
             if (configuration.TryGetValue("startNodeId", out var startNodeIdValue) &&
                 (!(startNodeIdValue?.ToString() is string startNodeId) || !Udi.TryParse(startNodeId, out _)))