Add recovery/startup test with backup_label and missing checkpoint segment

Add recovery/startup test with backup_label and missing checkpoint segment

This test is able to trigger the following failure at the beginning of
recovery, that was not covered yet:
FATAL:  could not locate required checkpoint record at %X/%X

Note that the backup used for the node created has its pg_wal/ removed,
which is why the segment expected is missing.

Extracted from a larger patch by the same author.

Author: Nitin Jadhav <nitinjadhavpostgres@gmail.com>
Discussion: https://postgr.es/m/CAMm1aWZ9Tv=Wrx52_2Ppw+6ULf_twRZuQm=ZWLA_a-kXWykHkQ@mail.gmail.com