Prevent stateless processes from serving as coordinators

FDB allows defining stateless processes that cannot run stateful roles, and it is generally safe to run these processes without a persistent volume. Running processes that way may be desirable on some infrastructure setups, such as when running FDB on Kubernetes. There is a risk that one of these stateless processes could be recruited as a coordinator by a user who was not applying the correct safety checks themselves. If this were to happen, it could leave the cluster in a state where processes restarting could cause a loss of a quorum of coordinators, which leaves the database in an unrecoverable state. As a protection against this, can we prevent stateless processes from serving as coordinators?

The issue names no files or tests. Start by tracing coordinator recruitment and the stateless-process role checks, then identify coverage for coordinator eligibility; done means stateless processes cannot be selected as coordinators and the relevant tests pass.

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