HHH-19584 add @CurrentTimestamp(allowMutation)

[gavinking]

[Please describe here what your change is about]

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license
and can be relicensed under the terms of the LGPL v2.1 license in the future at the maintainers' discretion.
For more information on licensing, please check here.

---

https://hibernate.atlassian.net/browse/HHH-19584

[gavinking]

@yrodiere This is the only significant thing here.

[yrodiere]

LGTM, thanks, but should we merge this immediately, or do you want someone to have a look at the "manually set the value for inserts" case too?
Asking because that might change the exposed API, if we decide its' better (simpler) to expose a single allowOverride() attribute controlling whether people can manually set the value for both inserts and updates.

[gavinking]

LGTM, thanks, but should we merge this immediately, or do you want someone to have a look at the "manually set the value for inserts" case too?

Well, nobody actually asked for that yet. (Except you 😉)

Asking because that might change the exposed API, if we decide its' better (simpler) to expose a single allowOverride() attribute controlling whether people can manually set the value for both inserts and updates.

It's not linked directly to inserts vs updates, it depends on whether the client can override generation. So I think it's two different things.

All that said, we can't merge this without a test.