docs(optimize): create migration guide for 3.12 (#3058)

* docs(optimize): create migration guide for 3.12

* style(formatting): technical review

* chore(docs): clarified removal of 8.8 support

* update translation diff

* update translation diff

---------

Co-authored-by: Christina Ausley <christina.ausley@camunda.com>
Co-authored-by: Josh Windels <joshua.windels@camunda.com>

optimize/self-managed/optimize-deployment/migration-update/3.11_8.3-to-3.12_8.4.md

@@ -0,0 +1,34 @@
+---
+id: 3.11_8.3-to-3.12_8.4
+title: "Update notes (8.3/3.11 to 8.4/3.12)"
+---
+
+:::note Heads up!
+To update Optimize to version 8.4/3.12, perform the steps in the [migration and update instructions](./instructions.md).
+:::
+
+The update to 8.4/3.12 can be performed from any 8.3/3.11 release.
+
+Here you will find information about:
+
+- Limitations
+- Known issues
+- Changes in supported environments
+- Changes in behavior (for example, due to a new feature)
+- Changes in translation resources
+
+## Changes in supported environments
+
+### Elasticsearch
+
+With 8.4/3.12, Optimize now supports Elasticsearch `8.9`. Elasticsearch `8.8` is no longer supported.
+
+If you need to update your Elasticsearch cluster, refer to the general [Elasticsearch update guide](https://www.elastic.co/guide/en/elasticsearch/reference/current/setup-upgrade.html). Usually, the only thing you need to do is perform a [rolling update](https://www.elastic.co/guide/en/elasticsearch/reference/current/rolling-upgrades.html).
+
+### Localization file
+
+The following terms have been added to or removed from the localization file `en.json` since the last release:
+
+[en.json.diff](./translation-diffs/differences_localization_311_312.diff)
+
+- Lines with a `+` in the beginning mark the addition/update of a term; lines with a `-` mark the removal of a term.

optimize/self-managed/optimize-deployment/migration-update/instructions.md

@@ -8,12 +8,12 @@ Optimize releases two new minor versions a year. These documents guide you throu
 
 If you want to update Optimize by several versions, you cannot do that at once, but you need to perform the updates in sequential order. For instance, if you want to update from 2.5 to 3.0, you need to update first from 2.5 to 2.6, then from 2.6 to 2.7, and finally from 2.7 to 3.0. The following table shows the recommended update paths to the latest version:
 
-| Update from  | Recommended update path to 8.3/3.11                               |
-| ------------ | ----------------------------------------------------------------- |
-| 8.3/3.11     | You are on the latest version.                                    |
-| 3.0 - 3.10.x | Rolling update to 8.3/3.11                                        |
-| 2.0 - 2.7    | 1. Rolling update to 2.7 <br /> 2. Rolling update from 2.7 to 3.0 |
-| 1.0 - 1.5    | No update possible. Use the latest version directly.              |
+| Update from      | Recommended update path to 8.3/3.11                               |
+| ---------------- | ----------------------------------------------------------------- |
+| 8.4/3.12         | You are on the latest version.                                    |
+| 3.0 - 8.3/3.11.x | Rolling update to 8.4/3.12                                        |
+| 2.0 - 2.7        | 1. Rolling update to 2.7 <br /> 2. Rolling update from 2.7 to 3.0 |
+| 1.0 - 1.5        | No update possible. Use the latest version directly.              |
 
 ## Migration instructions