Adds mlModelVersionDelete graphql mutation

What does this MR do and why?

Adds a new graphql action to delete ml model versions.

How to set up and validate locally

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

   Feature.enable(:model_registry)
   p = Project.find_by_id(1)
   model =  Ml::CreateModelService.new(p, "gitlab_amazing_model").execute.payload
   Ml::CreateModelVersionService.new(model, { version: "1.0.0" }).execute

2. Navigate to <gdk>/-/graphql-explorer, and execute the following mutation (replace values with your project and model id):

   mutation {
     mlModelVersionDelete(input: { id: "gid://gitlab/Ml::ModelVersion/1" }){
       errors
     }
   }

3. Model should be deleted without returning errors

Related to #428910 (closed)