Show project secrets table in CI/CD settings

What does this MR do and why?

#⃣ For #470373, #477573

Move project secrets table into CI/CD settings

Add Secrets settings section between Artifacts and Variables
Duplicate entry point for vue app into it
Redirect navigation away from the index route to /-/secrets

Why? We want to do a closed experiment for the GitLab Native Secrets Manager without adding a sidebar item yet, so we decided that the entry point for it will be a table in CI/CD settings. Taking any action to create/view/edit a secret will navigate over to the "main" secrets app.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After
	New section: Secrets (Experiment)
	Expanded view shows secrets table
	Screen_Recording_2024-08-08_at_18.33.02 - Any navigation away from the list (clicking on a secret, clicking edit in the actions menu, clicking New secret) takes you to /-/secrets (and using pagination does not) - Any navigation back to the list (clicking on the Cancel button, clicking on the Secrets breadcrumb, using the back button) takes you back to CI/CD settings

How to set up and validate locally

git checkout move-project-secrets-into-ci-cd-settings
echo "Feature.enable(:ci_tanukey_ui)" | gdk rails c

1. navigate to a project
2. in the sidebar, choose Settings => CI/CD
3. expand the Secrets section
4. the secrets table should be there
5. using the pagination below the table should not navigate away
6. any other action should navigate to the appropriate route within /-/secrets (with a full page load)
7. on routes in /-/secrets, any navigation action that goes back to the table should take you back to /-/settings/ci_cd with the Secrets section expanded

to run relevant tests

yarn install && yarn jest ci/secrets
bundle exec rspec ee/spec/features/projects/settings/secrets_settings_spec.rb ee/spec/helpers/secrets_helper_spec.rb