draft FreeBSD support

[dch]

This is a draft PR with the goal of supporting as much of simplomon
on FreeBSD as possible. We'll likely make a few further changes
in the next fortnight.

• ✅ addNtfyNotifier

• ✅ dns: check for expected RR

• ✅ dailyChime

• ✅ https: already expired cert thanks https://expired.badssl.com/

• ✅ https: minCertDays expiring soon expired cert

• ✅ https: 503 status

• ✅ https: ipv4 & ipv6

• ✅ dnssoa: servfail

• ✅ rrsig: sweet

• 💩 ping

• ✅ httpredir: works, but if fromUrl has trailing / we get an alert redir: Could not access path '' on server 'skunkwerks.at' for redir check, see httpredir: Fix fromUrl parser to correctly extract d_frompath #59 for fix

• ☃ addEmailNotifier can't test without auth, see Add SMTPS and SMTP AUTH support for EmailNotifier, through libcurl #34

• ☃ don't have an IMAP to test against yet

• ☃ I presume SMTP/STARTTLS check worked -- smtp{server="in1-smtp.messagingengine.com"} for fastmail, but using from/to seemed to work even though no email was sent

installing on FreeBSD

# pkg install -r FreeBSD pkgconf py311-pip libnghttp2 lua53 cmake nlohmann-json cpp-httplib xxd meson libfmt
# git clone https://github.com/skunkwerks/simplomon -b fix/freebsd
# cd simplomon
# LDFLAGS="-static-libstdc++ -static-libgcc" meson setup build --prefer-static meson setup build -Dbuildtype=release
# meson compile -C build/
# cp build/simplomon /usr/local/bin/