Archive the cdt-infra repo (#8)

See eclipse-cdt/cdt-infra#66 where all content
on master deleted in preparation for archiving and
eclipse-cdt/cdt-infra#67 where the readme was
added/restored.

otterdog/eclipse-cdt.jsonnet

@@ -66,6 +66,7 @@ orgs.newOrg('eclipse-cdt') {
       ],
     },
     orgs.newRepo('cdt-infra') {
+      archived: true,
       allow_merge_commit: true,
       allow_update_branch: false,
       default_branch: "master",