Changes mlModelDelete to mlModelDestroy

What does this MR do and why?

Changes only the mutation name, both have the same schema. This change is backwards compatible. No UI is changed.

How to set up and validate locally

1. In rails console enable the experiment fully and create a model and model version

   Feature.enable(:model_registry)
   
   p = Project.find_by(id: 1)
   Ml::CreateModelService.new(p, "model_1").execute 

2. Visit the project where the model was created

3. Click on Deploy > Model registry, and navigate to the created model

4. Click on the overflow menu, than on delete, and verify the model is deleted.

Related to #461047 (closed)