Issues related to running sidekiq-cluster by default

In #239 (closed) we've made running sidekiq-cluster the default for running Sidekiq in omnibus. I'll link this issue from the deprecation warnings there so users have a place to turn if something breaks.

Additionally, we'll also use Sidekiq Cluster by default for Helm charts, so let's have this issue linked in the blogpost for a point of contact for any bugs.