Refactors model list UI

What does this MR do and why?

Model list components were not following the pattern in ml/model_registry. This MR renames ml_models_index.vue to index_ml_models.vue and moves it under ml/model_registry/apps. No visual or functional changes

How to set up and validate locally

1. On rails console, enable the feature flag and create some data

   Feature.enable("model_registry")
   p = Project.find_by(id: 20) # or whatever project you want to use for testing
   3.times { |i|  Ml::FindOrCreateModelService.new(p, "model_#{i}").execute }
   
   Ml::FindOrCreateModelVersionService.new(p, { model_name: "model_1", version: "1.0.0" }).execute
   3.times { |i| Ml::FindOrCreateModelVersionService.new(p, { model_name: "model_2", version: "1.2.#{i}" }).execute }

2. Navigate to /-/ml/models

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #385061 (closed)