deprecate config property org.hibernate.flushMode on AvailableSettings

[gavinking]

It's actually a JPA hint, and rightfully belongs on HibernateHints.

cc @Sanne

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[Sanne]

Personally I completely agree... it's a dangerous property, even though I can see the appeal in certain scenarious, e.g. fully read-only systems - although it would be perfectly viable to set per-session on whatever general utility people will use as Session factory so I don't think I'd miss the property, even in the far fetched scenarios.

However there seem to be people asking for it even in Quarkus, just happened recently again:

• Add quarkus property to set the hibernate flushmode quarkusio/quarkus#29604 (comment)

We might want to proceed with this anyway, but perhaps let's give them a chance to explain themselves first?
Or at least wait for some other team member's opinions - at least @sebersole ?

cc/ @yrodiere

[gavinking]

I mean, all that is fine, I don't care if we have a config property for this. But that config property has to be called something like:

hibernate.default_flush_mode

or even

hibernate.session.default_flush_mode

or whatever.

It can't be called org.hibernate.flushMode because that's not the name of a config property :-)