Assign organization owners

An Organization will need owners. Ownership represents a type of membership.

• Every Organization will require at least one owner.
• The user who creates the Organization will be assigned as the Organization owner.
• The Organizations::Organization::DEFAULT_ORGANIZATION should assign all admin users as owners.

Availability & Testing

Some testing scenarios to think about:

• That we do not grant someone access they shouldn't have because they've been made an organization owner (ability to see projects in another company because they're both in Organizations::Organization::DEFAULT_ORGANIZATION). See #423200 (comment 1683547706)
• Performance impacts of the migration, during the migration?

Plan

• Add a new access_level column(enum) to organization_users with a default setting for the access_level in the database. !140817 (merged)
• Add user who creates the organization as the owner. !140817 (merged)
• Add data migration to add all admin users to organization_users as owner access_level for the default organization. !141297 (merged)
• Add logic to add user to organization_users as owner for the default organization when added or updated to an instance admin !141297 (merged)
• Add logic to downgrade from a default user in organization_users for the default organization when user is updated to not be an instance admin. !141297 (merged)
• Add logic to add user to organization_users as a default user for the default organization on user creation. maybe !141297 (merged)
• Define access_level access in policies. !139188 (merged)
• Rollout update_default_organization_users feature flag via #437896 (closed)
• Remove the Feature Flag update_default_organization_users - !142975 (merged)
• Reschedule instance admin backfill - !142979 (merged)