add an option to override the AMQP connection hostname value only

[gemmellr]

Adds an option to override the AMQP connection Open hostname in isolation.

It is already possible to override it and the SNI value with the virtualhost option, but you cant control it in isolation with vertx-amqp-client as the route to do so from vertx-proton to isnt usable here because pre-opened connections are returned on creation).

[gemmellr]

Stems from discussion on https://github.com/smallrye/smallrye-reactive-messaging/pull/1075 and https://github.com/quarkusio/quarkus/issues/15229

[cescoffier]

Thanks!

It would need to be backported to the 3.9 branch

[gemmellr]

Yep, I was waiting for the review before picking it, will push and pick it now.

[cescoffier]

Thanks!