pgsql: Add minimal tests for recovery conflict handling.

Add minimal tests for recovery conflict handling.

Previously none of our tests triggered recovery conflicts. The test is
primarily motivated by needing tests for recovery conflict stats for shared
memory based pgstats. But it's also a decent start for recovery conflict
handling in general.

The only type of recovery conflict not tested yet are rcovery deadlock
conflicts.

By configuring log_recovery_conflict_waits the test adds some very minimal
testing for that path as well.

Author: Melanie Plageman <melanieplageman@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20220303021600.hs34ghqcw6zcokdh@alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9f8a050f68dcb38fb0a1ea87e0e5d04df32b56f4

Modified Files
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src/test/recovery/t/031_recovery_conflict.pl | 296 +++++++++++++++++++++++++++
1 file changed, 296 insertions(+)