make add subnets from other AZ so that Fargate can be multi-az

[chaws]

AWS had an outage last morning where Fargate services got affected for us-east-1 region. Since all our computing power is allocated dynamically with Fargate, we couldn't scale up properly and I couldn't perform a roll out (running migrations need new pods).

I thought of adding more subnets in different az yesterday, but given the circumstances, I opted for not doing so.