Add non-blocking MR widget for external status checks

app/assets/javascripts/reports/constants.js

ee/app/assets/javascripts/reports/components/issue_body.js

...ets/javascripts/reports/status_checks_report/constants.js

...eports/status_checks_report/status_checks_reports_app.vue

...rge_request_widget/components/status_check_issue_body.vue

...avascripts/vue_merge_request_widget/mr_widget_options.vue

...cripts/vue_merge_request_widget/stores/mr_widget_store.js

ee/app/presenters/ee/merge_request_presenter.rb

...serializers/ee/merge_request_poll_cached_widget_entity.rb

...ures/merge_request/user_sees_status_checks_widget_spec.rb

...port/__snapshots__/status_checks_reports_app_spec.js.snap

ee/spec/frontend/reports/status_checks_report/mock_data.js

...ts/status_checks_report/status_checks_reports_app_spec.js

.../vue_mr_widget/components/status_check_issue_body_spec.js

ee/spec/frontend/vue_mr_widget/ee_mr_widget_options_spec.js

ee/spec/presenters/merge_request_presenter_spec.rb

locale/gitlab.pot