Allow multiple create cluster pipelines to run at once

[jaskaransarkaria]

Background

At the minute we have a bottleneck where only one test cluster can be created at once, this is sometimes annoying and slows dev work. Allow multiple runs at the same time. To guard against clusters having the same name we need to introduce an identifier, generate a unique id using the user who triggered the runs name and an additional uid (if needed)

[mikebell]

https://github.com/ministryofjustice/cloud-platform-terraform-concourse/tree/new-create-cluster-pipeline << start of this work is here.

Just needs more testing and then can replace the create cluster pipeline.