Is your feature request related to a problem? Please describe.

X509 certificate files often contain the leaf certificate and all intermediate CA certificates excluding the root. Fluentd should support such files, otherwise only certificates signed directly by the root CA can be used.

Describe the solution you'd like

Load all certs in the provided file into the OpenSSL context.

Describe alternatives you've considered

The only alternative is to issue certificates directly from the root, which is bad practice.

Additional context

About to open a PR - this issue is mostly for documentation purposes.