Add gRPC support for ibc-transfer/getEscrowAddress

[minxylynx]

Summary

From this issue #189 came the escrow-address cli function. It would be most useful for end users to have a grpc query route as well.

Problem Definition

As an end-user, I'd like to know what the escrow address is for a particular channel. Using cli isn't feasible when a web app wants to query via gRPC. I have a function that mimics how the escrow address is created, but that won't withstand future changes to the address creation.

Proposal

Add a gRPC route to get the escrow address for a channel, using the same inputs as the CLI.

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[crodriguezvega]

• Add definition for gRPC escrow-address method in transfers query.proto with route:

rpc EscrowAddress(QueryEscrowAddressRequest) returns (QueryEscrowAddressResponse) {
  option (google.api.http).get = "/ibc/apps/transfer/v1/escrow_address/port/{port_id}/channel/{channel_id}";
}

with request/response messages:

message QueryEscrowAddressRequest {}

message QueryEscrowAddressResponse {
  string escrow_address = 1;
}

• Implement method in transfer's grpc_query.go

[crodriguezvega]

This is now available in v3.1.0, v2.3.0 and v1.5.0.