(DON'T MERGE) [OC-5408] Add support for agent cluster leave

Created by: iamjazzar

This change introduces two things:

1. The ability to communicate with Consul through APIs directly without a need for external library. This is useful when we run into advanced cases where the library we're using doesn't support them.
2. Consul leave functionality which asks the agent to leave the cluster gracefully, or to instruct the agent to force a node into the left state if the agent couldn't leave its cluster gracefully.

I wanted to implement a multi-(threading|processing) approach here since the operation takes about 5-8 seconds to complete, then I backed of when I saw there's no such usage in the whole project for any of the approaches.

• Tests