Split up template_test.go

https://gitlab.com/gitlab-org/cluster-integration/auto-deploy-image/-/blob/master/assets/auto-deploy-app/test/template_test.go is getting unwieldy - at over 1000 lines - it is getting hard to navigate.

Proposal

• Split up tests by template, following the templates we have in assets/auto-deploy-app/templates e.g.
  • deployment_test.go
  • ingress_test.go
  • worker_deployment_test.go

/cc @shinya.maeda @hfyngvason WDYT ?