Record some Nginx log fields as numbers
Record some Nginx log fields as numbers

These fields should only ever be numbers; double and long. Recording them as
such instead of casting to strings will allow us to do more sophisticated
analysis in Kibana.

We can't apply the same to `gzip_ratio` or `upstream_response_time` because
they may be presented as `-` or multiple values.

The indicies in ElasticSearch will take 24 hours (when `es-rotate` runs) to
change from "string" to the field appropriate type. Testing with es-head
doesn't indicate any issues searching on these mixed types during the
interim period.

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