(#43475347) Change retention periods for Graphite
(#43475347) Change retention periods for Graphite

Rename existing default to match the statsd data that we currently hold
under the top-level keys:

- stats
- stats_counts
- statsd

Create a new default with a 10s immediate resolution to match collectd's
interval. Adjust future retentions to a sensible rate, which will create
whisper files of about 2.5M a piece.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet