tls: openssl: Load /etc/ssl/certs/ca-bundle.crt on RHEL. (#2974)
tls: openssl: Load /etc/ssl/certs/ca-bundle.crt on RHEL. (#2974)

Red Hat provides system CA certificates in a bundled form (a.k.a.
ca-bundle.crt). Unfortunately, OpenSSL's CAPath feature cannot
handle such a packed cert well.

This is the root problem of bug#2973: "TLS connections are always
broken on Amazon Linux".

This mitigates the issue by teaching Fluent Bit to load `ca-bundle.crt`
(which RHEL provides in /etc/ssl/certs) if available.

Signed-off-by: Fujimoto Seiji <ef879192bb1e41d519c82cf76440dc8e9a530806@ceptord.net>
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