[DOCS] Add upgrading information for version 12.3.0

UPGRADING.md

@@ -1,3 +1,24 @@
+# v12.2 to v12.3
+
+## For admins
+
+### Change TypoScript Paths For Templates
+TYPO3 v12 compatibility requires changes in the TypoScript configuration.
+The TypoScript path `module.tx_in2publish.view` can no longer be used to overwrite templates.
+Please read [60149-Change-TypoScriptPathsForTemplates.md] for details on how to adjust your TypoScript configuration.
+
+### Change .yml configuration files
+Up to version 12.2, the Content Publisher used the YAML parser [Spyc] for parsing the configuration files. Since TYPO3
+now ships with a YAML parser, we now use this parser to reduce the code we have to maintain.
+This change has some impact on the configuration files.
+Please read [60149-Change-ReplaceSpycWithSymfonyYaml.md] for details on how to adjust your configuration files.
+
+
+## For developers
+
+The core events `PublishingOfOneRecordBegan` and `PublishingOfOneRecordEnded` were replaced. Please
+read [54638-Deprecation-PublishingOfOneRecordBegan_Ended.md](Documentation/Developers/Changelog/54638-Deprecation-PublishingOfOneRecordBegan_Ended.md).
+
 # v12.1 to v12.2
 
 ## For developers