Enable admin to rename Issue Board default column names
User Story
As an admin of a GitLab projects, I want to rename the default columns in an Issue Board (such as "Backlog"), so that they do not clash with the use of that same name for other purposes (such as a "Backlog" milestone or "Backlog" label).
Elaboration
Brought up here and here. Push off as technical debt.
The main idea is that the admin should be in control of their namespaces within the nouns defined by GitLab, hence milestones and labels used for specific purposes (e.g., Issue Board columns) have default names, but those names are mutable by an admin.