pgsql: ci: Test NetBSD and OpenBSD

ci: Test NetBSD and OpenBSD

NetBSD and OpenBSD Postgres CI images are now generated [1], but aren't yet
utilized for Postgres' CI. This commit adds CI support for them.

For now the tasks will be manually triggered, to save on CI credits.

[1] https://github.com/anarazel/pg-vm-images

Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/CAN55FZ32ySyYa06k9MFd+VY5vHhUyBpvgmJUZae5PihjzaurVg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e291573534237c154609f320d774ef293c0cd2ee

Modified Files
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.cirrus.tasks.yml   | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++
.cirrus.yml         | 10 ++++++
src/tools/ci/README |  2 +-
3 files changed, 103 insertions(+), 1 deletion(-)