Audio player metrics aligned with .org code

[thomaswilburn]

Most metrics from the in-site player are detailed here:

https://github.com/npr/www/blob/master/templates/javascript/player/persistent/util/metrics/metrics.js

Custom dimensions are spelled out here:

https://github.com/npr/www/blob/master/templates/javascript/metrics/model.js

We probably don't have to match most of the events, since a lot of UI options (scrubbing, stream complete, etc.) aren't available to people listening on the liveblog. But there's enough to align with the standard playback duration and play/pause events.

[thomaswilburn]

Additional notes from Confluence docs:

• Event labels should be "liveblog-stream"
• Audio pings (duration) fire at 15s, 30s, 1m, 2m, 3m, 4m, 5m, and then every 5 minutes after that. Category is "audio pings", action is the "X sec ping" or "X min ping"
• Playback events - Category: "audio actions" Action: "initiate/pause/resume audio"