Use CTAS approach for rebalancing the materialized view

[whitehawk]

Use CTAS approach for rebalancing the materialized view

Problem description:
Before this patch, in order to rebalance a materialized view, 2 steps were
required: the actual rebalance where distribution policy was updated, and the
refresh step to update the data in the materialized view. This approach had 2
problems with respect to usage in 'ggrebalance' tool for cluster shrink:

1. It could change the actual data in the materialized view before the cluster
   shrink, and after the shrink, if the view was not up-to-date. We intend to keep
   the logical data in the cluster not altered.
2. If a materialized view depends on another materialized view, there could be
   a race condition when doing the refresh, when we try to refresh based on the
   yet-not-refreshed one.

Fix:
Use the CTAS approach from the EXPAND TABLE specifically when we are rebalancing
a materialized view. It creates a temp table with a correct distribution policy,
where all data from the materialized view is copied, and then the relfilenode
of the materialized view is swapped with the temp table. It keeps the data as it
was before the rebalance, even if it was not up-to-date (therefore we will not
surprise the user with the not expected view content), and it eliminates
dependencies on other objects besides the materialized view itself.