unique identifers for hosting assets per type (#107)

Co-authored-by: Michael Hoennig <michael@hoennig.de>
Reviewed-on: https://dev.hostsharing.net/hostsharing/hs.hsadmin.ng/pulls/107
Reviewed-by: Marc Sandlus <marc.sandlus@hostsharing.net>

src/main/resources/db/changelog/7-hs-hosting/701-hosting-asset/7010-hs-hosting-asset.sql

@@ -41,6 +41,8 @@ create table if not exists hs_hosting.asset
     config              jsonb not null,
     alarmContactUuid    uuid null references hs_office.contact(uuid) initially deferred,
 
+    unique (type, identifier), -- at least as long as we need to be compatible to the legacy system
+
     constraint hosting_asset_has_booking_item_or_parent_asset
         check (bookingItemUuid is not null or parentAssetUuid is not null or type in ('DOMAIN_SETUP', 'IPV4_NUMBER', 'IPV6_NUMBER'))
 );