Release 2988

WHY: DFE sign in is a requisite part of the project
HOW: mimic what PAAS is doing with Routes using k8 ingress

Trello card

https://trello.com/c/8Pz4dmqP/668-enable-dfe-sign-in-on-aks-review-apps

Context

the aim is to create a similar dfe sign in functionality to that of paas on aks

Changes proposed in this pull request

added get_next_mapping_aks.sh which mimcs existing get_next_mapping.sh using ingresses

Guidance to review

make review_aks terraform-plan-aks PR_NUMBER=777