docs: add release-notes for 19.

Author: ziggie1984

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

@@ -75,6 +75,11 @@
   config settings to its own dedicated group. The old ones still work but will
   be removed in a future release.
 
+* [Deprecate `dust-threshold`
+config option](https://github.com/lightningnetwork/lnd/pull/9182) and introduce
+a new option `channel-max-fee-exposure` which is unambiguous in its description.
+The underlying functionality between those two options remain the same.
+
 ## Breaking Changes
 ## Performance Improvements