Merge branch '233434-cablett-create_epic_board' into 'master'

app/services/boards/create_service.rb

doc/api/graphql/reference/gitlab_schema.graphql

doc/api/graphql/reference/gitlab_schema.json

doc/api/graphql/reference/index.md

ee/app/graphql/ee/types/mutation_type.rb

ee/app/graphql/mutations/boards/epic_boards/create.rb

ee/app/models/boards/epic_board.rb

ee/app/policies/ee/group_policy.rb

ee/app/services/boards/epic_boards/create_service.rb

...hangelogs/unreleased/233434-cablett-create_epic_board.yml

ee/spec/graphql/mutations/boards/epic_boards/create_spec.rb

ee/spec/policies/group_policy_spec.rb

ee/spec/services/boards/create_service_spec.rb

ee/spec/services/boards/epic_boards/create_service_spec.rb

...examples/services/boards/create_boards_shared_examples.rb