🎨 Design: Moving from Admin Area to Organization for self-managed users

Problem

Currently all Organization-related functionality is feature flagged so that we can roll it out on GitLab.com specifically to start with. However, in the mid term we also want to enable Organizations for self-managed customers. As a lot of the existing Admin Area functionality is going to move to Organizations, we need to decide what we want the User Experience to be during this transition. See also: 🎨 Design: Transition to Organization for self-m... (#383267). Could we define what an iterative transition for self-managed customers would look like? How could Admin Area and Organization co-exist while functionality is moved from one to the other?

Challenge: We expect migration of Admin Area features to take a long time. Customer needs would drive which features and settings are migrated first. We want to avoid leaving one feature flag in place for too long, so need to decide how we can iteratively release these changes to Organizations using separate feature flags for each migration.

Note: The Admin Area will probably never cease to exist and remain a place a to host hardware settings and an Organization overview.

Proposal

Phase1 - Organization MVC

Organization	Admin	Navigation
Organization has features and settings defined in the MVC designs	Admin stays as it is today Admin content is driven by the Org context switcher Some features (ie users) are not affected by the Org context switcher and are sourced from the instance	Context switcher Admin link goes to admin as it does today

Phase2 - Transition phase

Organization	Admin	Navigation
Features are moved from Admin to the organization iteratively Features are copied from groups where applicable	Features are removed (moved) from admin iteratively	Unchanged

Phase3 - Transition phase complete

Organization	Admin	Navigation
All applicable admin and group features have been moved/copied to the Organization	All applicable admin and features have been removed (moved) to the Organization	Unchanged

Admin settings during the transition phase

Example admin setting as it exists today	Example admin setting that has been moved to an organization in a multi-organization instance	Example admin setting that has been moved to an organization in a single-organization instance

As settings are moved to the organization level they stay in the admin but are wrapped in an organization selector that is shown if the instance has multiple organizations.