test: no-op marker for 15.14 smoke baseline (do not merge)

This PR exists purely as a reference target for `supadev trigger-smoke-tests`
so we can run the smoke matrix against develop's current 15.14.1.132 /
17.6.1.132 / 17.6.0.089-orioledb AMIs. We're investigating whether the
storage tenant-migration race observed on the 15.18 utk_test AMI also
surfaces on current production builds (suggesting the race is environmental
rather than a 15.18 regression).

Refs: PSQL-1230

Author: utkarash2991

nix/docs/README.md

@@ -1,5 +1,7 @@
 # Documentation
 
+<!-- Cosmetic no-op marker (PSQL-1230): smoke-test baseline against develop. -->
+
 This directory contains most of the "runbooks" and documentation on how to use
 this repository.