BAP-21264: Add support of Elasticsearch 8.*

 - added upgrade documentation
 - added information to changelog

Author: yshyshkin

bundles/platform/ElasticSearchBundle/index.rst

@@ -19,7 +19,7 @@ OroElasticSearchBundle enables |Elasticsearch| as a :ref:`search engine <search_
    configuration
    request-builders
    troubleshooting
-   upgrade-to-es7
+   upgrade-to-es8
 
 .. include:: /include/include-links-dev.rst
    :start-after: begin

bundles/platform/ElasticSearchBundle/upgrade-to-es7.rst

@@ -0,0 +1,24 @@
+Upgrade Website Index to Elasticsearch >=8.3, <9.0
+==================================================
+
+You have only one option to perform the upgrade: via full reindexation.
+
+Keep in mind that the previous OroCommerce versions (5.0 and below) have different structure for
+flat object fields, so full indexation is required in order to fill the data in the correct format.
+
+Full Reindexation
+-----------------
+
+This option is suitable for upgrades from all previous versions.
+
+Search index upgrade is part of the :ref:`application upgrade <upgrade-application>`.
+So, once you have turned on maintenance mode through ``app/console lexik:maintenance:lock --env=prod``, you need to perform the following actions:
+
+1. |Stop old Elasticsearch|
+2. Modify credentials for search engine configuration in the `config/parameters.yml` file
+3. |Start the Elasticsearch| 8.\* service.
+
+Proceed with the :ref:`standard upgrade procedure <upgrade-application>`.
+
+.. include:: /include/include-links-dev.rst
+   :start-after: begin