Allow TAP tests to force checksums off when calling init()

Allow TAP tests to force checksums off when calling init()

TAP tests can write

    $node->init(no_data_checksums => 1);

to initialize a cluster explicitly without checksums.  Currently, this
is the default, but this change allows running all tests with
checksums enabled, like

    PG_TEST_INITDB_EXTRA_OPTS=--data-checksums meson test ...

And this also prepares the tests for when we switch the default to
checksums enabled.

The pg_checksums tests need to disable checksums so it can test its
own functionality of enabling checksums.  The amcheck/pg_amcheck tests
need to disable checksums because they manually introduce corruption
that they want to detect, but with checksums enabled, the checksum
verification will fail before they even get to their work.

Author: Greg Sabino Mullane <greg@turnstep.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://www.postgresql.org/message-id/flat/CAKAnmmKwiMHik5AHmBEdf5vqzbOBbcwEPHo4-PioWeAbzwcTOQ@mail.gmail.com