Add new key pairs for delivery service

[malteish]

I think we are using the same key pairs for delivery service and backend on staging atm. This has at least one unintended consequence: DS will accept backend auth JWTs and vice versa (same server secret). Therefore, we must generate new key pairs for at least one of the services. Since we are testing the setup of ds anyway, changing DS key pairs is the obvious choice.

Estimate: 0.5 days