PG17 compatibility: fix pg16 to pg17 upgrade

[colm-mchugh]

In citus_prepapre_upgrade(), don't drop any_value when upgrading from PG16+, because PG16+ has its own any_value function. Attempting to do so results in the error seen in pg16-pg17 upgrade:

ERROR:  cannot drop function any_value(anyelement) because it is required by the database system
CONTEXT:  SQL statement "DROP AGGREGATE IF EXISTS pg_catalog.any_value(anyelement)"

When 16 becomes the minimum supported Postgres version, the drop statements can be removed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.61%. Comparing base (1bee8b0) to head (eef5d84).
Report is 1 commits behind head on naisila/pg17_support.

Additional details and impacted files

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##           naisila/pg17_support    #7788      +/-   ##
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+ Coverage                 89.59%   89.61%   +0.01%     
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  Files                       274      274              
  Lines                     59732    59716      -16     
  Branches                   7451     7449       -2     
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- Hits                      53518    53514       -4     
+ Misses                     4079     4066      -13     
- Partials                   2135     2136       +1     

[naisila]

Thanks for the fix, I remember I have implemented this so sorry for that mistake :)

However we can't merge as it is as we need to create a new .sql file for the new citus version. We don't modify old .sql files. I don't remember where the ocumentation for this part is, but basically we need to add a new 13.0-1.sql file with the modified script, and also an upgrade and downgrade path for Citus https://github.com/citusdata/citus/tree/release-13.0/src/backend/distributed/sql

[colm-mchugh]

However we can't merge as it is as we need to create a new .sql file for the new citus version. We don't modify old .sql files. I don't remember where the ocumentation for this part is, but basically we need to add a new 13.0-1.sql file with the modified script, and also an upgrade and downgrade path for Citus https://github.com/citusdata/citus/tree/release-13.0/src/backend/distributed/sql

The latest push reverts the modification to the existing citus sql file and adds a new one; however it probably needs #7792 to enable the pg16 -> pg17 upgrade to pass (?)