Set default Entity to "ACTION" in InsertObject

Added XML summary to Entity property describing valid values.
Changed default value from null to "ACTION" for clarity.

src/ReC.Application/Common/Procedures/InsertObject.cs

@@ -4,5 +4,8 @@ namespace ReC.Application.Common.Procedures;
 
 public record InsertObject : IRequest<long>
 {
-    public string Entity { get; set; } = null!;
+    /// <summary>
+    /// Target entity: ACTION, ENDPOINT, ENDPOINT_AUTH, ENDPOINT_PARAMS, PROFILE, RESULT
+    /// </summary>
+    public string Entity { get; set; } = "ACTION";
 }