[4.3] test support for partition key annotation

[roguebee-droid]

I've added a fairly straightforward test for partition key #3108 based on what is in hibernate-orm

Hibernate-orm does have some more tests for this annotation for specific databases as well as association which I haven't done here but could add if required.

[DavideD]

Why this PR contains changes to TimeStampTest?

[roguebee-droid]

My previous issue fix is on my main branch which I branched off, want to leave that as it is till it's merged into yours rather than potentially mess up that issue. I'm going to rebase to an earlier commit and do the changes to that, then force them onto this branch. You might need to reopen this pull request again as that could auto close the pull request. Sorry about this, learning experience with github.

[DavideD]

Thanks a lot.

I don't think this test is enough, though. The problem is that I can remove the annotation and it doesn't fail.
I think you can solve it by checking the native queries generated by the test. They should contain a where clause related to the annotated column.
You can probably mimic the test in Hibernate ORM: PartitionKeyTests

Although, in Hibernate Reactive we have a different way to check SQL queries, you can find an example here:
You can see an example in FetchedAssociationTest.

Because the queries will use standard SQL, I think it should work on all databases even if you are testing native queries.

The Hibernate ORM documentation has an example of the SQL looks like: Section 3.11.1 Partitioning

[DavideD]

See my previous comment: #3262 (comment)