Concourse: Increase worker CPU limits

[sj-williams]

Background

Our Concourse workers are regularly hitting the defined CPU limits and getting throttled:

Increase the CPU limits for workers, test applying the change on a test concourse cluster for any service impact.

• [ ] readme has been updated
• [ ] user docs have been updated
• [ ] another team member has reviewed
• [ ] smoke tests are green
• [ ] prepare demo for the team

Reference

How to write good user stories

[sj-williams]

concourse worker limits PR: https://github.com/ministryofjustice/cloud-platform-terraform-concourse/pull/381

infra: https://github.com/ministryofjustice/cloud-platform-infrastructure/pull/3139