Support RestEasy reactive for Quarkus extension

[peteroyle]

For the future of the Quarkus extension support #2279 I think we should either switch to purely Reactive (since Classic is effectively deprecated) or start supporting both the Classic and Reactive RestEasy deployment modes.

I'm in two minds about which to choose.

1. Given the relatively low uptake of the Elide Quarkus extension, now might be a good time to hitch ourselves to the Reactive wagon and save ourselves the effort of supporting Classic going forward. If we were to choose this option, should we do it in the next patch release, or wait for at least a point release?

2. On the other hand, those using the Elide Quarkus extension right now may have been encouraged into using RestEasy Classic because that's the only mode supported by Elide Quarkus currently. Forcing a difficult migration to Reactive as the price of upgrading Elide Quarkus may alienate what few supporters we currently have.

I have a PR ready that implements option 1, but I'd be happy to rework it if option 2 is preferred. In the meantime I'd love to hear everyone's thoughts on the matter.