pgsql: Add recovery test for missing redo segment with backup_label

Add recovery test for missing redo segment with backup_label

This commit adds a test case for early startup where a backup_label file
uses a checkpoint LSN and a redo LSN located in two different segments,
where the segment of the redo LSN is missing. This code has never been
covered, and is complex enough that a test case is going to be useful in
the long-term.

Nitin has proposed a more complex approach than what is added by this
commit, by forcing a reuse of the injection points to produce a split
between redo and checkpoint. This commit relies on the checkpoint and
redo LSNs generated by the first steps of the test, combined with a
generated backup_label, making the whole cheaper.

Author: Nitin Jadhav <nitinjadhavpostgres(at)gmail(dot)com>
Author: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/CAMm1aWZ9Tv=Wrx52_2Ppw+6ULf_twRZuQm=ZWLA_a-kXWykHkQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8f71f64deee6747ad9dea18819018b25424d61e5

Modified Files
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src/test/recovery/t/050_redo_segment_missing.pl | 44 +++++++++++++++++++++++++
1 file changed, 44 insertions(+)