Follow up - Add Vuex to customizable cycle analytics

Summary

Migrate api calls and state management for customizable cycle analytics to vuex:

• We are introducing Vuex to cycle analytics as part of the group level analytics refactor - merged
• We are also introducing customizable stages to cycle analytics - merged
• We will be introducing additional api requests with the new cycle analytics backend

This should be completed after the group level refactor and customizable stages form UI are merged.

Improvements

• We will have consistent state management through all of cycle analytics

Risks

• Customizable cycle analytics

Involved components

• We can remove: ee/app/assets/javascripts/analytics/cycle_analytics/components/custom_stage_form_container.vue
• Additional state, actions, getters, mutations and mutation types will be added for labels and events

Optional: Intended side effects

Optional: Missing test coverage

• Additional test for vuex actions, mutations, getters etc