[api] Define standard property for handling duplicated keys

[lukasj]

taken out from #240:

by @jjspiegel

One could imagine a duplicate keys handling option that accepts something like USE_FIRST, USE_LAST, REJECT

by @rmannibucau

I'd like it to be jakarta.json.rejectDuplicateKeys instead (with true/false/ values in the map config of the related factories - default being false).

[jbescos]

• TCK