Implement RPC health_check endpoint

[stdevMac]

Is your feature request related to a problem? Please describe. We should implement an health_check endpoint like this one on the Nethermind client

Describe the solution you'd like Create a new RPC endpoint, that can be fixed, query the sync status, and any other info from the node. For more details, reach @stdevMac.

[tshakalekholoane]

I think this should be namespaced for consistency so maybe something like juno_healthCheck. See the following examples.

[tshakalekholoane]

One of the fields returned should probably also be an indicator of the number of blocks synced so that the user knows the range blocks they can execute calls against.