Remove PostgreSQL service after deprecation (#589)

* manually remove postgresql service

* remove examples and go work references

* add note to changelogs

Author: DiogoFerrao

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## Release (2024-XX-XX)
 
+> **The STACKIT PostgreSQL service has reached its end of support on June 30th 2024. All calls done to the API have stopped working since then.**
+>
+> Use `github.com/stackitcloud/stackit-sdk-go/services/postgresflex` instead. For more details, check https://docs.stackit.cloud/stackit/en/bring-your-data-to-stackit-postgresql-flex-138347648.html.
+
 - `postgresflex`: [v0.15.0](services/postgresflex/CHANGELOG.md#v0150-2024-06-28)
   - **Feature**: New API methods `CreateDatabase`, `DeleteDatabase`, `ListDatabase`, `ListDatabaseParameters` to manage PostgreSQL Flex databases
   - **Feature**: New API method `UpdateInstance` to update the instance

examples/postgresql/go.mod

@@ -18,7 +18,6 @@ use (
 	./examples/objectstorage
 	./examples/opensearch
 	./examples/postgresflex
-	./examples/postgresql
 	./examples/rabbitmq
 	./examples/redis
 	./examples/resourcemanager
@@ -41,7 +40,6 @@ use (
 	./services/objectstorage
 	./services/opensearch
 	./services/postgresflex
-	./services/postgresql
 	./services/rabbitmq
 	./services/redis
 	./services/resourcemanager