graph/db: handle topology updates in a single location

In this commit, we ensure that any topology update is forced to go via
the `handleTopologySubscriptions` handler so that client subscriptions
and updates are handled correctly and in the correct order.

This removes a bug that could result from a client missing a
notification about a channel being closed if the client is subscribed
and shortly after, `PruneGraph` is called which would notify all
subscribed clients and possibly do so before the client subscription has
actually been persisted.

docs/release-notes/release-notes-0.19.0.md

@@ -128,6 +128,9 @@ when running LND with an aux component injected (custom channels).
   such that the probability is evaluated quicker and to be more accurate in
   outdated scenarios.
 
+* [Fix a bug](https://github.com/lightningnetwork/lnd/pull/9798) that could
+  result in a new topology client missing a channel-close notifications. 
+
 # New Features
 
 * Add support for [archiving channel backup](https://github.com/lightningnetwork/lnd/pull/9232)