MVC1: Vue-based labels lists

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1. Display labels in Vue-based list (behind Feature flag)
2. Add sorting
   • Will need to add support for sort options through graphql
3. Add searching (graphql already supports)
4. Add subscription filter
   • Likely need new graphql support for subscribed labels
5. Add label actions
   1. Users can delete a label (has existing Vue components)
   2. Users can promote a label to the next hierarchy level (has existing Vue components)
   3. Users can access the edit page (haml version in this iteration)
   4. Users can view issues/MRs using the label (just links to filtered list)
6. Add link to create label
7. Add prioritized labels functionality
   1. Users can mark a label as prioritized from the main list
   2. Users can view ordered list of prioritized labels
   3. Users can reorder prioritized labels from the prioritized labels view
   4. Users can remove prioritization from a label from either main list or prioritized list
8. Enable feature flag for verification
9. Remove feature flag