refactor(sns): Add global lock for the periodic tasks that relates to upgrades

[anchpop]

This is useful because there's no benefit to allowing periodic tasks that relate to upgrades to be interleaved with one another, and allowing it actually complicates things somewhat because we need to constantly think about what states can arise from various interleaving. As is our standard, we have a 10-minute expiry on the lock so that it's unlikely that it will accidentally get locked forever.