Added a show labels to the merge request dashboard

...ts/merge_request_dashboard/components/config_dropdown.vue

...ipts/merge_request_dashboard/components/merge_request.vue

app/assets/javascripts/merge_request_dashboard/index.js

..._request_dashboard/queries/merge_request.fragment.graphql

app/views/dashboard/merge_requests.html.haml

...events/click_toggle_labels_on_merge_request_dashboard.yml

...ser_id_from_toggle_labels_off_merge_request_dashboard.yml

...user_id_from_toggle_labels_on_merge_request_dashboard.yml

...ount_total_merge_request_dashboard_labels_toggled_off.yml

...count_total_merge_request_dashboard_labels_toggled_on.yml

...erge_request_dashboard/components/config_dropdown_spec.js

.../merge_request_dashboard/components/merge_request_spec.js

spec/frontend/merge_request_dashboard/mock_data.js