Use vue-router for Iteration Cadences

What does this MR do?

• Add vue-router on top of !59227 (merged)
• Add placeholder component for the 'List' view so router can actually do something
• Change cadencesListPath from a prop to provide/inject, as it does not need reactivity
• Change the selector suffix from -form to -app, since we could be rendering either component

Progress:

1. Add HAML and boilerplate - !59216 (merged)
2. Add initial form - !59227 (merged)
3. Add vue router (this MR) - !60725 (merged)
4. Fix vue-router breadcrumbs
5. Add List page - !61096 (merged)
6. Add Edit page

What does it not do?

• breadcrumbs (copy approach from registry_breadcrumb)
• meta title update

How to test

• enable :iteration_cadences feature flag
• visit <group>/-/cadences/new to create a cadence
• get redirected to a blank page (list page with no content)