docs(open-banking): Update Open Banking certificate/key mapping documentation

**Description**
[Ticket-440](https://help.gluu.org/agent/tickets/440)
The Open Banking configuration documentation currently lists the required certificates/keys and their purposes, but the mapping between these files and the corresponding override.yaml properties is not clear.

We should update the documentation to include a dedicated Override Property Name column showing which global property in override.yaml is used for each certificate/key.

**Documentation**

https://docs.gluu.org/stable/openbanking/install-cn/#install-using-helmproduction-ready