UI to display Candidate metadata

What does this MR do and why?

We were storing mlflow tags as CandidateMetadata, but there was no UI do display this metadata. This is the simplest UI possible to achieve that.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the feature flag

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

2. Create an Experiment, Candidate and Metadata (use project id for a chosen project):

   exp = Ml::Experiment.create!(name: "Gitlab Experiment", user_id: user_id, project_id: project_id)
   exp.candidates.create!(user_id: user_id, start_time: 0) }
   5.times { |i| c.metadata.create!(name: "metadata#{i}", value: "content#{i}") }
   c.metrics.create!(name: "auc", value: 0.1 , tracked_at: Time.zone.now, step: 1)
   c.metrics.create!(name: "accuracy", value: 0.1 , tracked_at: Time.zone.now, step: 1)
   c.params.create!(name: "algorithm", value: "DecisionTree" )
   puts(exp.candidates[0].iid)

3. Navigate to <your project>/-/ml/candidates/<candidate_iid>

MR acceptance checklist

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

Related to #383986 (closed)