replace go uuid generation by postgresql

backend/internal/db/migrations/008_uuid_default.down.sql

@@ -0,0 +1 @@
+ALTER TABLE files ALTER COLUMN id DROP DEFAULT;

backend/internal/db/migrations/008_uuid_default.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE files ALTER COLUMN id SET DEFAULT gen_random_uuid();
+ALTER TABLE files ALTER COLUMN storage_key SET DEFAULT '';