Acquisition of multiple connections for schema management

[yrodiere]

Hibernate Reactive seems to acquire several connections for schema management, which can lead to deadlocks in some extreme situations (small connection pool, multiple schema management running concurrently on the same pool).

See quarkusio/quarkus#39930 (comment)

We could fix it by avoiding the use of multiple concurrent transactions in schema update script generation in Hibernate ORM and/or Hibernate Reactive.
For Hibernate Reactive, weirdly it seems to acquire a connection to then immediately ignore it and acquire a second one from the pool in selectJdbcOutsideTransaction. That's probably a bug @DavideD , isn't it? At the very least I'd expect the first connection not to be acquired.