Introduce a self-referential many-to-many relation table so a
third party can have child third parties. Each relation is
directional (parent to child); both directions can coexist as
independent rows.
Add a first_level boolean on third_parties (default true) with
a filter on the list page that defaults to showing only
first-level third parties.
Frontend adds a "Third Parties" tab on the detail page where
users can link existing third parties or create new ones from
the common third party catalog (created as non-first-level).
The list page gets a First Level/All toggle filter.
Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>
b6b1e801b1