Add Redis configuration
Add Redis configuration

This is required so that asset manager's sidekiq instance can store
its queues in redis[1]

[1] https://github.com/alphagov/govuk_sidekiq#4-configure-puppet

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