Dotnet Etcd Versions Save

1. Randomize balancing of node connections
2. Add timeout and cancellation token support
3. Fix exception stacktrace
4. Update packages

Handle watch exceptions in every case

1. Add Support for multiple cluster endpoints (#19)
2. Add dotnet core 3.0, standard 2.1 support
3. Update packages

1. Update balancer logic
2. Fix header injections

#19 - Add etcd cluster endpoints support.

Implemented : https://github.com/etcd-io/etcd/blob/master/Documentation/learning/design-client.md

#18 - Exposed lease ttl from etcd client

1. Add support for Auth operations
2. Inject Headers in all requests
3. Add snapshot support in maintenance calls
4. Add LeaseKeepAlive support
5. Fix rpc exception loop