docs: Add release notes for PR dashpay#6708

Documents the change to enable BIP157 block filters by default.

Author: PastaPastaPasta

doc/release-notes-6708.md

@@ -0,0 +1,6 @@
+Updated settings
+----------------
+
+- BIP157 compact block filters are now enabled by default. This improves privacy for light clients
+  and enables better support for pruned nodes. The `-blockfilterindex` option now defaults to `basic`
+  instead of `0` (disabled), and the `-peerblockfilters` option now defaults to `true` instead of `false` (#6708).