Instrument json-rpc server and json-rpc client and capture appropriate metrics

[alexghr]

Add instrumentation to the JSON-RPC layer:

Server:

metric	type	attributes
number of requests	counter	service name (e.g. node, pxe, prover node), rpc method (e.g. getTips)
number of errors	counter	service name, rpc method
rpc duration	histogram	service name, rpc method
request span	span	link against parent span from client

Client:

metric	type	attributes
number of requests	counter	host, service name, rpc method (e.g. getTips)
number of errors	counter	host, service name, rpc method
request size in bytes	gauge	host, service name, rpc method
response size in bytes	gauge	host, service name, rpc method
rpc duration	histogram	host, service name, rpc method
request span	span	link against parent span from client