Add iteration cadences list

What does this MR do?

Add basic list page for iteration cadences.

Requires the :iteration_cadences feature flag, adds content to gdk.test:3000/groups/gitlab-org/-/cadences page

MRs

1. Add HAML and boilerplate - !59216 (merged)
2. Add Vue form - !59227 (merged)
3. Add vue router !60725 (merged)
4. Add basic List page [this MR] - !61096 (merged)
5. Add collapsible cadence sections to list page - !61546 (merged)
6. Add Edit page

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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Security

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