Set up toolchain version manager

This issue is an follow up of #29. Without a toolchain version manager, developers running different versions of the toolchain, especially golang and protoc, could run into conflicts.

One example is the generated protobuf code such as [blockchain.pb.go](https://github.com/coinbase/chainstorage/blob/master/protos/coinbase/chainstorage/blockchain.pb.go).

As proposed by @bestmike007 we may leverage [asdf](https://asdf-vm.com/) to manage the toolchain version.