Merge branch 'revert-multi-select' into 'master'

app/assets/javascripts/boards/components/board_card.vue

app/assets/javascripts/boards/components/board_list.vue

app/assets/javascripts/boards/constants.js

app/assets/javascripts/boards/index.js

app/assets/javascripts/boards/models/list.js

app/assets/javascripts/boards/services/board_service.js

app/assets/javascripts/boards/stores/boards_store.js

app/assets/javascripts/test_utils/index.js

app/assets/stylesheets/pages/boards.scss

app/controllers/groups/boards_controller.rb

app/controllers/projects/boards_controller.rb

doc/user/project/img/issue_boards_multi_select.png

doc/user/project/issue_board.md

ee/changelogs/unreleased/multi-select-move.yml

locale/gitlab.pot

spec/features/boards/multi_select_spec.rb

spec/javascripts/boards/board_card_spec.js

spec/javascripts/boards/boards_store_spec.js