Document that the quarkus-reactive-routes extension is deprecated in RHBQ 2.13

In order to preserve compatibility for customers who use an earlier release of RHBQ, we will productize and ship the quarkus-reactive-routes extension in RHBQ 2.13, but we also deprecate it in favor of the Reactive Routes extension form Vert.x.
In terms of support obligations, we are going to support both extensions in RHBQ 2.13, but we want to indicate to developers that they should move to using the one from Vert.x.

Please reach out to cescoffi@redhat.com for more information.