chore: add derpserver to wsproxy, add proxies to derpmap (#7311)

coderd/database/migrations/000142_proxy_derp.down.sql

@@ -0,0 +1,15 @@
+BEGIN;
+
+-- drop any rows that aren't primary replicas
+DELETE FROM replicas
+	WHERE "primary" = false;
+
+ALTER TABLE replicas
+	DROP COLUMN "primary";
+
+ALTER TABLE workspace_proxies
+	DROP CONSTRAINT workspace_proxies_region_id_unique,
+	DROP COLUMN region_id,
+	DROP COLUMN derp_enabled;
+
+COMMIT;