Replace issues list page Haml search bar and list with Vue
`issuable_list` component under the feature flag `vue_issues_list`.

This change:

- Adds missing UI elements to `issuable_item.vue` for issues
- Adds pagination

Subsequent MRs will:

- Add sorting
- Add searching
- Add filtering
- Add missing filtered-search tokens
- Add empty state
- Add bulk edit