Expand Sparkplug Aware MQTT Server definition to include automatic expansion of DATA and BIRTH metric content into individual topics

[wes-johnson]

This came from a list of suggestions in #432.

[RickBullotta]

This would be considered a "Sparkplug aware broker" capability of course. I think one key consideration here is how the root topic is mapped to a Sparkplug Group/Node. That should be something configurable at the broker level I'd think, and if not defined the topics would look like:

/\<GroupID>/\<NodeID>/\<MetricName>

and

/\<GroupID>/\<NodeID>/\<MetricName>/_metadata

I would also suggest that these auto-expanded topics always be published with the retain flag set.