Allow users to delete candidates

What does this MR do and why?

Reuses DeleteButton to allow users to delete a candidate. Upon deletion, users are redirected to the experiment page.

Screenshots or screen recordings

	Before	After
Page
Modal

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 and a candidate

   user_id = 1 # if you are using root
   project_id = 20 # not necessarily 20, but the project you are using for testing
   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)

3. Navigate to the candidate "/path_to_project/-/ml/candidates/1"

4. Click on the dropdown, click on "Delete candidate", confirm the modal.

5. Verify that you were redirected to "/path_to_project/-/ml/experiments/1", and that the experiment has no candidates

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.