Add option to bind to loop packet instead of archive record about weewx-mqttsubscribe

[bellrichm]

Better is to bind to both. The archive event could check whether it is hardware or software generation. If software, StdArchive would accumulate the loop packet. If hardware, this service would have to.
After processing the loop packet, is the data put on a separate queue?
Is it put into an accumulator? If so, would the need to be shuffled like inStdArchive? I think so.

[bellrichm]

With record augmentation, should only need to emit loop packets.

[bellrichm]

Decided for either/or binding. In general, I think that binding to the loop makes more sense and is the default.
By binding to the loop, the QC functions of WeeWX "just work" and record augmentation would then add it to the archive record. But there is more overhead because for each loop packet, the MQTT data must be accumulated.