QUIC Retry generation relies on global cluster-secret to produce token
valid even after a process restart and across several LBs instances.
Before this patch, Retry is automatically deactivated if no
cluster-secret is provided. This is the case even if a user has
configured a QUIC listener with quic-force-retry. Change this behavior
by now returning an error during configuration parsing. The user must
provide a cluster-secret if quic-force-retry is used.
This shoud be backported up to 2.6.
996ca7d0fa