ADBDEV-5527: Explain Analyze doesn't show statistics for queries with DML inside CTE

[mos65o2]

Change the portal strategy for modifying CTE case

In vanilla PG and Greenplum queries containing modifying CTE are executed
with portal strategy PORTAL_ONE_MOD_WITH, which involves storing the result
of the query in portal's tuple store, which the final result is then fetched
from. This strategy is fair enough and helps us avoid executing
modifying operation several times, for example, when one need to fetch
the query result partially. However, in Greenplum case executing this
strategy at QE nodes is redundant, because clients communicate with the
system throught the QD node. Therefore, this commit proposes another
type of strategy for execution at QE nodes.

Moreover, when a query contains modifying CTE, EXPLAIN ANALYZE reports most of
plan nodes as "never executed", even though the corresponding nodes have been
fully executed and have returned the tuples. This problem arise because
of PORTAL_ONE_MOD_WITH execution strategy, according to which the extra
pq message with tuple description is sent to QD, and the statistics
can't be retrieved properly in cdbexplain_recvExecStats function.

Changes cherry-pick commit: updated test outputs and matchsubs.

(cherry picked from commit c9b7b02)

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Commits in the PR shouldn't be squashed to preserve authorship.

[silent-observer]

Please specify changes from the original commit in the new commit description (just "updated test outputs and matchsubs", if I didn't miss anything else)

[silent-observer]

LGTM