In this PR we are introducing the last piece of the push interaction model in which every node monitors their health and sends it to the health node in the following situations:

• when it changes from the last reported state
• when there is a new health node

Implementation details

To synchronize the code we use an atomic reference to the last successfully reported health info. This variable gets updated in the following ways:

• it gets updated if the health info was successfully received by the health node and last reported value hasn't changed since this method read from it.
• it gets reset (set to null without any preconditions) when there is a change in the health node. Effectively, when the health node changes, the health node doesn't have any health data so it makes sense for the last successfully reported health info to be null too.