INSERT to Iceberg tables from Impala

[Zoltán Borók-Nagy]

Hi,

I'm willing to add INSERT support for Iceberg tables in Impala.

For start I created the following design doc:
https://docs.google.com/document/d/1_KL0YptDKwhiXvJyx4Vb-yZjggrPQAW2yjeGV4C0vMU/edit?usp=sharing

All comments are welcome.

Thanks,
    Zoltan