pgsql: Log more info when wait-for-catchup tests time out.

Log more info when wait-for-catchup tests time out.

Cluster.pm's wait_for_catchup and allied subroutines don't provide
enough information to diagnose the problem when a wait times out.
In hopes of debugging some intermittent buildfarm failures, let's
dump the ending state of the relevant system view when that happens.

Add this to v17 too, but not stable branches.

Discussion: https://postgr.es/m/352068.1723422725@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2aecbd752616aa664f32b3c1804732e475def7cc

Modified Files
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src/test/perl/PostgreSQL/Test/Cluster.pm | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)