document the caveats in timezone-aware timestamps support for Oracle python clients

[ivasio]

Documentation description

There seems to be a long-standing issue in python/C driver support of timezone-aware timestamps for Oracle. Namely, if the column is defined as TIMESTAMP WITH TIME ZONE, both cx_Oracle and oracledb truncate timezone info in select results. Impact of that should be studied and documented, in particular for to incremental and reflection_level. Ideally, specific warnings should also be printed

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