docs: added front-coded dictionaries to upgrade notes (#16647)

* docs: add front-coded dictionareis to upgrade notes

* add it to release notes template

docs/release-info/release-notes.md

@@ -97,6 +97,19 @@ This section contains detailed release notes separated by areas.
 
 ### Upgrade notes
 
+#### Front-coded dictionaries
+
+<!--Carry this forward until 32. Then move it to incompatible changes -->
+
+In Druid 32.0.0, the front coded dictionaries feature will be turned on by default. Front-coded dictionaries reduce storage and improve performance by optimizing for strings where the front part looks similar.
+
+Once this feature is on, you cannot easily downgrade to an earlier version that does not support the feature. 
+
+For more information, see [Migration guide: front-coded dictionaries](./migr-front-coded-dict.md).
+
+If you're already using this feature, you don't need to take any action. 
+
+
 ### Incompatible changes
 
 ### Developer notes

docs/release-info/upgrade-notes.md

@@ -26,6 +26,18 @@ The upgrade notes assume that you are upgrading from the Druid version that imme
 
 For the full release notes for a specific version, see the [releases page](https://github.com/apache/druid/releases).
 
+## Announcements
+
+#### Front-coded dictionaries
+
+In Druid 32.0.0, the front coded dictionaries feature will be turned on by default. Front-coded dictionaries reduce storage and improve performance by optimizing for strings where the front part looks similar.
+
+Once this feature is on, you cannot easily downgrade to an earlier version that does not support the feature. 
+
+For more information, see [Migration guide: front-coded dictionaries](./migr-front-coded-dict.md).
+
+If you're already using this feature, you don't need to take any action. 
+
 ## 30.0.0
 
 ### Upgrade notes