Adds initial frontend component for Model registry

What does this MR do and why?

Adds the initial code for the Model Registry UI.

This MR does not work on the UX yet, it is just setting up for future MRs. Things that will be added later:

• pagination
• search
• more info about each model

This feature is behind a feature flag. See [model_registry] Feature flag rollout issue (#385047 - closed).

Screenshots or screen recordings

Before	After
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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Enable the feature flag

   echo "Feature.enable(:model_registry)" | bundle exec rails c

2. Create a few packages of model type. In rails console:

   project = Project.find_by(id: 1) # or any other project you are testing
   project.packages.create!(name: 'model1', version: 'a', package_type: :ml_model)
   project.packages.create!(name: 'model1', version: 'b', package_type: :ml_model)
   project.packages.create!(name: 'model2', version: 'a', package_type: :ml_model)

3. Navigate to /-/ml/models, should display a json version of the models with the name, version and path of each of them. Note that only one model1 should be displayed.

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)