HTTP long poll based deployment

[sazid]

PR Type

Refactor

PR Checklist

• Tests for the changes have been added / updated.
• A changelog entry has been made.
• Version number has been updated.
• Required modules have been added to respective "requirements*.txt" files.
• (Team) Label with affected action categories and semver status.

Overview

THIS IS A BREAKING RELEASE for server-node communication (node internal logic).
Test cases or no other behavioral change is expected. Server upgrade is mandatory.

This PR replaces the websocket based deployment model with a newer
HTTP long poll based deployment system. This has the following
implications:

1. Will work on any enterprise scenarios where websocket support is limited.
2. Will work on unstable network connections where websocket would often drop connections. Although node could reconnect by itself, it was still problematic.
3. New implementation is a lot simpler to understand and hence possible bugs.
4. Reduced tons of complexity in the connection code.
5. Removed usages of protocol buffers. Which means, clients can directly consume and interact with node/test case data in plain json format instead of having to rely on the protobuf files.