Add docs for new RPC: peer_connection_healthcheck

[onur-ozkan]

Related PR: KomodoPlatform/komodo-defi-framework#2194

Example request:

curl -s -w '\n Request speed: %{time_total}s\n' --url "http://127.0.0.1:7783" --data '{
  "userpass":"'$userpass'",
  "method":"peer_connection_healthcheck",
  "mmrpc":"2.0",
  "params": {
	  "peer_address": "12D3KooWCcjBQ3kG3BzjVwuZqGDL2YxXik6SCDv2YAHj4E54NiAy"
  }
}'

Example response:

{"mmrpc":"2.0","result":true,"id":null}

[smk762]

Closed by #356