[docs] XA Transactions section is not accurate

[zhfeng]

https://docs.quarkiverse.io/quarkus-artemis/dev/index.html#_xa_transactions

XA Transactions must be activated on a per-configuration basis, they are not enabled by default.

To activate XA transactions, we can set quarkus.artemis.xa-enabled / quarkus.artemis."named-configuration".xa-enabled to true.

IIRC, quarkus.artemis.xa-enabled is only used to expose XAConnectionFactory. So in the user application, it can be injected like

@Inject
XAConnectionFactory xaCF;

And this does not active a XA transaction. Currently, if users want to use JMS connection in a XA transaction, the quarkus-pooled-jms has to be introduced in pom.xml and set quarkus.pooled-jms.transaction=xa.