Add information about namespace encoding to API docs
What does this MR do?
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/25722
Replaces Contribution MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8307
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/25722
Replaces Contribution MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8307