Improves user and MR display on Candidate Detail

What does this MR do and why?

Follow up from !119788 (merged), improves how user and MR are displayed:

• User is displayed with a labeled avatar
• MR is displayed with its title

Screenshots or screen recordings

Before	After

How to set up and validate locally

Set up is a bit cumbersome, as you will need to create a Merge request to have the pipeline (or use one that you already created)

1. Enable the feature flag

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

2. Create a Merge request on a project

3. Create an experiment and a candidate (in rails console)

   user_id = 1 # if you are using root
   project_id = 1 # not necessarily 1, but the project you created the merge request on
   exp = Ml::Experiment.create!(name: 'Gitlab Experiment', user_id: user_id, project_id: project_id)
   c = exp.candidates.create!(user_id: user_id, start_time: 0, internal_id: 1, project_id: project_id)

4. Associate the candidate with a job from the merge request (in rails console)

   project_id = 1 # not necessarily 1, but the project you created the merge request on
   merge_request_id = 1 # or the id of your merge request
   c = Ml::Candidate.by_project_id_and_iid(project_id, 1)
   c.ci_build = MergeRequest.by_id(merge_request_id).head_pipeline.builds[0]
   c.save!

5. Navigate to the candidate "/path_to_project/-/ml/candidates/1". Verify the CI rows are showing as the new version

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 #411910 (closed)