add option to enable TLS via environment variable

[victoru]

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[edsiper]

@victoru thanks for this contribution.

I am wondering if enabling TLS is enough for certification validation, is Fluent Bit able to validate Elasticsearch certificate properly by default ?

[victoru]

By default, I'd say yes. Fluent bit was able to validate the certificate when I used it with an AWS Elasticsearch cluster.

[edsiper]

please rebase on top of master

[sbrandtb]

@edsiper Merge this? I've also implemented this in my local copy the same way

[mwl]

This seems to have stalled a bit. Is there anything you need help with? (We kind of need this)