Reuse gRPC connections instead of creating new ones

[Pitasi]

Very similar to this api-server issue: EmerisHQ/demeris-api-server#108.

I would expect to only have one gRPC connection per chain. What we're currently doing instead is:

sdk-service/grpc_cosmos_sdk_v42.go

Line 64 in a409a12

grpcConn, err := grpc.Dial(fmt.Sprintf("%s:%d", chainName, *port), grpc.WithInsecure())

DoD:

• store connections, we can use the chain URL as key (fmt.Sprintf("%s:%d", chainName, *port)), gRPC can probably be configured to reconnect on failures so this store should never expire
• store the "clients": e.g.

  sdk-service/grpc_cosmos_sdk_v42.go

  Line 73 in a409a12

  bankQuery := bank.NewQueryClient(grpcConn)

  , since we have a single connection, there's no need to initialize new clients every time

⚠️ we are currently lacking a service mesh that will load balance requests among the available replicas (since we use a long lived TCP connection we remain connected to a single pod)

[akhilkumarpilli]

Blocked with https://github.com/EmerisHQ/infra/issues/9