Add Group Boards feature specs

Feature specs are present for project issue boards on https://gitlab.com/gitlab-org/gitlab-ee/blob/master/spec/features/boards/boards_spec.rb. The same specs should also be tested for group issue boards, if possible we could move specs of the file above into shared examples and use them for group and project boards.

The following discussion from !31481 (merged) should be addressed:

• @felipe_artur started a discussion: (+5 comments)

  @winh this is the backport of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14973

  @acroitor Can you review it too please?

  Also i could not find feature specs for group issue boards on CE/EE. We have it only for project issue boards spec/features/boards/boards_spec.rb. We should consider opening another follow up issue for it.