howto: import kata logs with fluentd

Document examples of how to import Kata logs with `fluentd`.
Show examples both from the systemd/logfmt method and the
file/JSON method.

Fixes: kata-containers#601

Depends-on:github.com/kata-containers/tests/pull/2334

Signed-off-by: Graham Whaley <[email protected]>

Author: Graham Whaley