UX Improvements - Experiment List

What does this MR do and why?

Experiments List had poor UX, this improves it a bit. This also moves Pagination from page to keyset.

Screenshots or screen recordings

	Before	After
With Experiments
Empty State

How to set up and validate locally

1. Enable feature flag

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

2. Open <SOME_PROJECT_PATH>/-/ml/experiments. It should show the empty state

3. Create some data:

   # Added variables
   project_id = <ID FOR SOME_PROJECT>
   
   exp1 = Ml::Experiment.create!(name: "Awesome Gitlab Experiment", user_id: nil, project_id: project_id)
   exp2 = Ml::Experiment.create!(name: "Awesome Gitlab Experiment2", user_id: nil, project_id: project_id)

4. Open <SOME_PROJECT_PATH>/-/ml/experiments. It should show the experiments

Database

https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/15253/commands/53088

SELECT
    ml_experiments.*,
    count(ml_candidates.id) AS candidate_count
FROM
    "ml_experiments"
    LEFT OUTER JOIN "ml_candidates" ON "ml_candidates"."experiment_id" = "ml_experiments"."id"
WHERE
    "ml_experiments"."project_id" = 21
GROUP BY
    "ml_experiments"."id"
ORDER BY
    "ml_experiments"."id" DESC
LIMIT 21

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 #387509 (closed)