Enable discarded event records snapshot FT DST feature by default

Enable discarded event records snapshot FT DST feature by default

This patch changes `config.py` (API) and the v3 YAML parser to make
the discarded event records snapshot field type (data stream type)
feature enabled by default.

This feature is nice to have, only adds an integer field to each packet,
and doesn't require anything from the user.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>