Bump search-api unicorns to 48 per machine
Bump search-api unicorns to 48 per machine

I want to reduce the number of machines we have in production as it's
costing us money. Staging has 36 unicorns running on machines with half
the CPU and RAM of those in production (and seems fine).

The machines are under low load, and there's plenty of headroom in terms of
CPU and memory used. [Example machine on Grafana](https://grafana.production.govuk.digital/dashboard/file/machine.json?refresh=1m&orgId=1&var-hostname=search-ip-10-13-5-135_eu-west-1_compute_internal&var-cpmetrics=All&var-filesystem=All&var-disk=All&var-tcpconnslocal=All&var-tcpconnsremote=All&from=now-2d&to=now)

I propose to ratchet this up in stages, to potentially halve the number of
machines eventually.

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