Merge branch 'ntepluhina-mr-assignees-widget' into 'master'

...l_shared/queries/users_search_with_mr_permissions.graphql

...ascripts/sidebar/components/assignees/assignee_avatar.vue

...pts/sidebar/components/assignees/assignee_avatar_link.vue

.../sidebar/components/assignees/collapsed_assignee_list.vue

...ripts/sidebar/components/assignees/issuable_assignees.vue

...sidebar/components/assignees/sidebar_assignees_widget.vue

...s/sidebar/components/assignees/sidebar_invite_members.vue

...ipts/sidebar/components/assignees/sidebar_participant.vue

app/assets/javascripts/sidebar/constants.js

app/assets/javascripts/sidebar/mount_sidebar.js

...components/sidebar/queries/get_mr_assignees.query.graphql

...ents/sidebar/queries/update_mr_assignees.mutation.graphql

...scripts/vue_shared/components/user_select/user_select.vue

app/assets/stylesheets/pages/issuable.scss

app/controllers/projects/merge_requests_controller.rb

.../assets/javascripts/boards/components/assignee_select.vue

.../merge_request/user_creates_multiple_assignees_mr_spec.rb

...es/merge_request/user_edits_multiple_assignees_mr_spec.rb

ee/spec/frontend/boards/components/assignee_select_spec.js

spec/features/issues/issue_sidebar_spec.rb