Adjust max_prepared_transactions only when it is default

[Green-Chan]

DESCRIPTION: Adjusts max_prepared_transactions only when it's set to default on PG >= 16

Fixes #7711.
Change AdjustMaxPreparedTransactions to really check if max_prepared_transactions is explicitly set by user, and only adjust max_prepared_transactions when it is default.
This fixes 021_twophase test failure with loaded Citus library after postgres/postgres@b39c5272.

[Green-Chan]

Argh, I always forget to check it with older PG versions. find_option is declared static in guc.c, so it won't work. Check using find_options for PG versions >= 16, and keep the old check for older versions is too ugly, isn't it?

[onurctirtir]

Two questions:

1. Why do we provide "create_placeholders" as "true"?
2. Should we provide "elevel" as "ERROR" maybe?

[Green-Chan]

Thank you for your comments. I no longer remember why. Right now providing "create_placeholders" as "false" and "elevel" as "ERROR" looks better to me, and it seems to work. Fixed that, rebased to main, and squashed my commits

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 48.72%. Comparing base (bb9d90e) to head (c5d8c40).
Report is 1 commits behind head on main.

❌ Your patch status has failed because the patch coverage (50.00%) is below the target coverage (75.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project status has failed because the head coverage (48.72%) is below the target coverage (87.50%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (bb9d90e) and HEAD (c5d8c40). Click for more details.

HEAD has 81 uploads less than BASE

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Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7712       +/-   ##
===========================================
- Coverage   89.20%   48.72%   -40.48%     
===========================================
  Files         283      283               
  Lines       61051    60150      -901     
  Branches     7625     7411      -214     
===========================================
- Hits        54458    29308    -25150     
- Misses       4408    28211    +23803     
- Partials     2185     2631      +446     

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[Green-Chan]

@onurctirtir , what is your policy on back-porting that kind of changes to released versions? Is it going to get to 13.0 and 12.1? Or it will only get to the future version (13.1, 14.0, or whatever it is)?