Add client field for IdP and SSO

add a field client number for IdP and match it with translate5 client so that SSO through external application can point to translate5 users assigned to different clients.

The field name for client number in the SSO should be configurable.

So far for the default client the "translate5 domain" can not be configured and the openid configuration can not be set.

This should change so, that the translate5 domain is preset with the currently configured main domain for the instance (unchangeable) and that openid can be configured.

Also the tool tip for the client number field must explain, that if it is filled, the mapping of incoming user is done with the client, that is transferred there instead of via translate5 domain. And if the client does not exist, it is created. And if the client number field in SSO exists but it is empty, then the mapping is done via the URL to which the client belongs (current behavior). The tooltip should be on the client number form field and its label.

Tooltip:

DE: Die OpenID-Connect-Implementierung von translate5 ermöglicht es, einen Client auf der IDP-Seite einem Client in translate5 zuzuordnen. Die Zuordnung erfolgt über die Kundennummer. Weitere Informationen finden Sie in der Dokumentation von translate5.

EN: The OpenID Connect implementation of translate5 makes it possible to assign a client on the IDP side to a client in translate5. The assignment is made via the client number. Further information can be found in the translate5 documentation.