cookie support in Ethereum::HttpClient

[shao1555]

Motivation

I'm operating several Ethereum server instances behind load balancer such as ELB.
some JSON-RPC methods such as filter related functions should process by same backend instance.

e.g. eth_newFilter and eth_getFilterChanges requests should be execute in same instance.

To resolve this problem, using cookie based session affinity feature to load balancer, then make this client compatible for its feature.

Resolution

Handles set-cookie header if call with cookie: true header.
This implementation is very limited, lack of some basic implementation such as expiration and persistence.

Reference

• Target Groups for Your Application Load Balancers - Elastic Load Balancing > Sticky Sessions
• Backend Services | Compute Engine Documentation | Google Cloud > Setting generated cookie affinity