making api usage guidelines public

Reviewed-by: Tino Schreiber <tino.schreiber@t-systems.com>
Co-authored-by: Hasko, Vladimir <vladimir.hasko@t-systems.com>
Co-committed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com>

otc_metadata/data/documents/apiu-guidelines.yaml

@@ -1,5 +1,4 @@
 ---
-environment: internal
 hc_location: api-usage/guidelines
 html_location: docs/apiu/guidelines
 link: /api-usage/guidelines/

otc_metadata/data/services/apiu.yaml

@@ -1,5 +1,5 @@
 ---
-environment: internal
+environment: hidden
 repositories:
 - environment: internal
   repo: docs/api-usage