Issue boards - Fetch recent board in GraphQL

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

...ascripts/boards/graphql/group_recent_boards.query.graphql

...cripts/boards/graphql/project_recent_boards.query.graphql

app/assets/javascripts/boards/index.js

...sets/javascripts/boards/mount_multiple_boards_switcher.js

.../assets/javascripts/boards/components/boards_selector.vue

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

ee/spec/frontend/boards/mock_data.js

spec/frontend/boards/components/boards_selector_spec.js

spec/frontend/boards/mock_data.js