Spec: Switch to patcg-id UD

Per discussion in speced/bikeshed-boilerplate#43
and #59, we should update the spec's group from patcg to patcg-id and
the status to UD.

This is blocked on the bikeshed-boilerplate PR linked above as well as
speced/bikeshed#2628.

spec.bs

@@ -2,8 +2,8 @@
 Title: Private Aggregation API
 Shortname: private-aggregation-api
 Level: 1
-Status: w3c/CG-DRAFT
-Group: patcg
+Status: UD
+Group: patcg-ig
 Repository: patcg-individual-drafts/private-aggregation-api
 URL: https://patcg-individual-drafts.github.io/private-aggregation-api
 Editor: Alexander Turner, Google https://www.google.com, [email protected]