Fix Cross Zone Routing in the ASEA On-Premise Subnet Route Table

**Describe the bug**
There is an issue in the ASEA central routing where cross AZ routes are being dropped. This results in intermittent 504s. This essentially means that our highly available routing network actually devolves to a single point of failure. We need to enable cross AZ routing in the on-premise subnet's route table in the Perimeter account. This means that we need to provide a route to the GWLB from aza to azb and azb to aza within the route table. See attached ticket for solution.

**Additional context**
This is the pull request Ryan J made to do this change: https://github.com/aws-samples/aws-secure-environment-accelerator/pull/1007

**Definition of done**
- [ ] config.json in Forge is changed so that the above will be automatically deployed
- [ ] State Machine is run in Forge
- [ ] config.json in Assembly is changed so that the above will be automatically deployed
- [ ] State Machine is run in Assembly
- [ ] config.json in Live is changed so that the above will be automatically deployed
- [ ] State Machine is run in Live