Limit which repositories this workspace may deploy from

Owner-only, and a replace: send the whole list. Exists because GitHub holds one repository selection per installation and several workspaces can share one, so narrowing it there narrows it for all of them. Holding the list here leaves GitHub’s selection alone. While restricted, a repository outside the list cannot be chosen, browsed or deployed — by a person, an API key or an operator — and a repository that is not on it is refused with a 404. repos/orgs omitted keeps the stored list. Refused (409) when an app here deploys from a repository or organisation the list omits, because that app would stop deploying; and (400) for a repository the caller cannot see on GitHub, or an organisation this workspace is not connected to.