Add support for hls loopback

[mcshicks]

It would be nice test hls audio without having to connect to S3 and have orcasound S3 AWS keys. One way to do this is to replace
s3_upload with something like

sleep 20
ffplay -nodisp /tmp/$NODE_NAME/hls/$timestamp/live.m3u8

keyed off a .env variable, perhaps the existing one NODE_LOOPBACK could have some additional value like HLS_LOOPBACK to support switching this on and off. This would be for all nodes types, dev/research/virtual/mseed