KML Export API for SondeHub

[darksidelemm]

I've seen a few requests around the traps for a way to get a KML file for a radiosonde.
We currently can do this for SondeHub-Amateur, but not for SondeHub. I expect this will only work with 'hot' data, and probably use mostly the same code as the sondehub-amateur KML export

[darksidelemm]

As per discussion:

• Bucket data to 1s intervals, will cut down on dupes before the JSON-to-KML conversion.
• This will need to go into something other than the /sonde/ query, which calls out to S3 for data not in ES.