docs(upgrade): add improvements to db-dependency of helm chart (#284)

docs/developer/Technical Documentation/Version Upgrade/portal-upgrade-details.md

@@ -1,4 +1,7 @@
 - [Summary](#summary)
+  - [vx.x.x](#vxxx)
+    - [OnboardingServiceProvider - ENHANCED](#onboardingserviceprovider---enhanced)
+    - [Postgres dependency of helm chart - ENHANCED](#postgres-dependency-of-helm-chart---enhanced)
   - [v1.8.0](#v180)
     - [Agreements - ENHANCED](#agreements---enhanced)
       - [Impact on existing data:](#impact-on-existing-data)
@@ -32,6 +35,8 @@ Each section includes the respective change details, impact on existing data and
 
 > **_INFO:_** inside the detailed descriptions below, the definition 'migration script' refers to the term 'migrations' as it is defined by the ef-core framework: https://learn.microsoft.com/en-us/ef/core/managing-schemas/migrations
 
+### vx.x.x
+
 #### OnboardingServiceProvider - ENHANCED
 
 - ENHANCED: table onboarding_service_provider_details "encryption_mode" added
@@ -100,6 +105,12 @@ to ensure the new encryption is able to decrypt preexisting client_secrets the o
 echo -n ")U\;>/h=ELj+.v5AD9(P2HQ3JnuYt.R:" | xxd -p
 ```
 
+#### Postgres dependency of helm chart - ENHANCED
+
+Be aware that the PostgreSQL version of the subchart by Bitnami of the [portal helm chart](https://github.com/eclipse-tractusx/portal) has been changed from 15.4.x to use the latest available version of 15.
+
+In addition, the fullnameOverride, which was set by default, has been removed which leads to a differently named database server. In case you would like to upgrade the PostgreSQL subchart, the fullnameOverride can either be applied by overwrite using an additional values.yaml file or by executing a blue-green deployment, as outlined below: [PostgreSQL Dependency - Upgrade](#postgresql---upgrade)
+
 ### v1.8.0
 
 #### Agreements - ENHANCED