Add JsonElementSerializer to MongoDB persistence provider

Fixes #4482

src/modules/Elsa.MongoDb/Features/MongoDbFeature.cs

@@ -1,3 +1,4 @@
+using System.Text.Json;
 using Elsa.Features.Abstractions;
 using Elsa.Features.Services;
 using Elsa.MongoDb.Options;
@@ -51,6 +52,7 @@ public class MongoDbFeature : FeatureBase
         BsonSerializer.RegisterSerializer(typeof(Type), new TypeSerializer());
         BsonSerializer.RegisterSerializer(typeof(Variable), new VariableSerializer());
         BsonSerializer.RegisterSerializer(typeof(Version), new VersionSerializer());
+        BsonSerializer.RegisterSerializer(typeof(JsonElement), new JsonElementSerializer());
     }
 
     private static void RegisterClassMaps()

src/modules/Elsa.MongoDb/Serializers/JsonElementSerializer.cs

@@ -0,0 +1,36 @@
+using System.Text.Json;
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization;
+
+namespace Elsa.MongoDb.Serializers;
+
+/// <summary>
+/// Serializes a <see cref="Type"/>.
+/// </summary>
+public class JsonElementSerializer : IBsonSerializer<JsonElement>
+{
+    /// <inheritdoc />
+    public Type ValueType => typeof(JsonElement);
+    
+    void IBsonSerializer.Serialize(BsonSerializationContext context, BsonSerializationArgs args, object value) => Serialize(context, args, (JsonElement)value);
+    object IBsonSerializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) => Deserialize(context, args);
+
+    /// <inheritdoc />
+    public JsonElement Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
+    {
+        if (context.Reader.CurrentBsonType == BsonType.Null)
+        {
+            context.Reader.ReadNull();
+            return new JsonElement();
+        }
+
+        var json = context.Reader.ReadString();
+        return JsonSerializer.Deserialize<JsonElement>(json);
+    }
+
+    /// <inheritdoc />
+    public void Serialize(BsonSerializationContext context, BsonSerializationArgs args, JsonElement value)
+    {
+        context.Writer.WriteString(value.GetRawText());
+    }
+}