remote-dev-cluster: add sa-east-1 region

[denisshevchenko]

Currently we have remote-dev-cluster with 3 core nodes in different AWS regions.

Unfortunately, the region we need - sa-east-1, South America (São Paulo) - isn't supported: https://github.com/NixOS/nixpkgs/blob/cda4a36eda3668858a39b8754db798520fba402c/nixos/modules/virtualisation/ec2-amis.nix#L295-L308.

It would be ideal if we were able to deploy one of 3 core nodes in sa-east-1, because in this case we'll get the worst possible network latency.

[CodiePP]

^^ this is the issue with the missing region @disassembler

[CodiePP]

in epic: input-output-hk/iohk-monitoring-framework#323