Multiple replicas of subnet router

[begemotik]

I noticed that the recent major release removed the possibility to configure multiple replicas.
What is the rationale behind that?

[Gowiem]

@begemotik we typically only use one subnet router that we deploy into each VPC or if we're using a Transit Gateway, we deploy a single subnet router into the centrally shared VPC that then routes through to all the others. We typically don't see the need to deploy two since the resiliency of the subnet router is accomplished through the auto-scaling group if something goes wrong. Were you deploying multiple subnet routers and found that useful? Want to describe your reasoning a bit more? We're not opposed to making this configurable, so happy to accept a PR to change this up!