pgsql: Allow passing extra options to initdb for tests

Allow passing extra options to initdb for tests

Setting the environment variable PG_TEST_INITDB_EXTRA_OPTS passes
extra options to initdb run by pg_regress or
PostgreSQL::Test::Cluster's init.

This can be useful for a wide variety of uses, like running all tests
with checksums enabled, or with JIT enabled, or with different GUC
settings, or with different locale settings. (Not all tests are going
to pass with arbitrary options, but it is useful to run this against
specific test suites.)

Reviewed-by: Ian Lawrence Barwick <barwick(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/d4d2ad9f-1c1d-47a1-bb4d-c10a747d4f15%40eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/995d400ceca3e552f84fe19f150fb03327bdc0c2

Modified Files
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doc/src/sgml/regress.sgml | 34 +++++++++++++++++++++++++-------
src/test/perl/PostgreSQL/Test/Cluster.pm | 7 +++++++
src/test/regress/pg_regress.c | 7 ++++++-
3 files changed, 40 insertions(+), 8 deletions(-)