Add third-party self-referential relations

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>

pkg/trust/third_party_service.go

@@ -65,7 +65,7 @@ func (s ThirdPartyService) ListForOrganizationId(
 		ctx,
 		func(ctx context.Context, conn pg.Querier) error {
 			showOnTrustCenter := true
-			filter := coredata.NewThirdPartyFilter(&showOnTrustCenter)
+			filter := coredata.NewThirdPartyFilter(&showOnTrustCenter, nil)
 
 			err := thirdParties.LoadByOrganizationID(ctx, conn, scope, organizationID, cursor, filter)
 			if err != nil {
@@ -99,7 +99,7 @@ func (s ThirdPartyService) CountForTrustCenterId(
 
 			thirdParties := &coredata.ThirdParties{}
 			showOnTrustCenter := true
-			filter := coredata.NewThirdPartyFilter(&showOnTrustCenter)
+			filter := coredata.NewThirdPartyFilter(&showOnTrustCenter, nil)
 
 			count, err = thirdParties.CountByOrganizationID(ctx, conn, scope, trustCenter.OrganizationID, filter)
 			if err != nil {