Additional Routes and support `cpu_architecture` override (e.g. for ARM64)

[cablespaghetti]

Adds additional routes which is something we need to have a single subnet router for our multiple VPCs. Also fixes #6 for good measure.

[dhermes]

@cablespaghetti Thanks for the contribution! I'll tag a release v1.20230203.1 right now that you can pin to!

UPDATE: Done

• https://github.com/hardfinhq/terraform-aws-tailscale-subnet-router/releases/tag/v1.20230203.1
• https://registry.terraform.io/modules/hardfinhq/tailscale-subnet-router/aws/1.20230203.1