Service templates page: Disable service template when instance-level integration is configured

Description

As part of the iteration 1 #213857 (closed), when an instance-level integration is configured, we have to disable the corresponding service template in the frontend.

Note: We also need to prevent to go directly to the URL of the service template. EDIT: I don't think this is needed. There is no harm if the user still wants to update the service template 🤷

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