Set hive.cbo.fallback.strategy to NEVER by default

The hive.cbo.fallback.strategy property defines when Hive fallbacks to legacy optimizer if an error occurs during the CBO phase.

At the moment the default value is CONSERVATIVE, which is the backward compatible option, and automatically fallbacks to legacy optimizer when certain errors occur.

The legacy optimizer is (hive.cbo.enable=false) is gonna soon be officially deprecated (HIVE-27830); unofficially it was treated as such for a long time now.

To reduce maintenance cost and improve CBO coverage and stability we should NEVER fallback to the legacy optimizer after a CBO error.

NEVER should be the default behavior in newer releases; users can still set the property to CONSERVATIVE as a temporary workaround till the CBO error is addressed.