policy: add a global boolean to enable tracing on policy matching

[MichaelMure]

I find that quite convenient, but not sure it has a place in the final code.

=== RUN   TestJsonRpc
=== RUN   TestJsonRpc/or_on_method,_not_matching
match ["==", ".jsonrpc.method", "eth_getCode"] --> False
match ["==", ".jsonrpc.method", "eth_getBalance"] --> False
match ["==", ".jsonrpc.method", "eth_call"] --> False
match ["==", ".jsonrpc.method", "eth_blockNumber"] --> False
match ["or", [
  ["==", ".jsonrpc.method", "eth_getCode"],
  ["==", ".jsonrpc.method", "eth_getBalance"],
  ["==", ".jsonrpc.method", "eth_call"],
  ["==", ".jsonrpc.method", "eth_blockNumber"]]]
 --> False
--- PASS: TestJsonRpc/or_on_method,_not_matching (0.00s)
=== RUN   TestJsonRpc/or_on_method,_matching
match ["==", ".jsonrpc.method", "eth_getCode"] --> False
match ["==", ".jsonrpc.method", "eth_getBalance"] --> False
match ["==", ".jsonrpc.method", "eth_call"] --> True
match ["or", [
  ["==", ".jsonrpc.method", "eth_getCode"],
  ["==", ".jsonrpc.method", "eth_getBalance"],
  ["==", ".jsonrpc.method", "eth_call"],
  ["==", ".jsonrpc.method", "eth_blockNumber"]]]
 --> True
--- PASS: TestJsonRpc/or_on_method,_matching (0.00s)
=== RUN   TestJsonRpc/complex,_optional_parameter,_matching
match ["==", ".jsonrpc.method", "debug_traceCall"] --> True
match ["==", ".jsonrpc.params[3]?", "callTracer"] --> True
match ["or", [
  ["==", ".jsonrpc.params[3]?", "callTracer"],
  ["==", ".jsonrpc.params[3]?", "prestateTracer"]]]
 --> True
--- PASS: TestJsonRpc/complex,_optional_parameter,_matching (0.00s)
=== RUN   TestJsonRpc/complex,_optional_parameter,_missing_parameter
match ["==", ".jsonrpc.method", "debug_traceCall"] --> True
match ["==", ".jsonrpc.params[3]?", "callTracer"] --> OptionalNoData
match ["or", [
  ["==", ".jsonrpc.params[3]?", "callTracer"],
  ["==", ".jsonrpc.params[3]?", "prestateTracer"]]]
 --> OptionalNoData
--- PASS: TestJsonRpc/complex,_optional_parameter,_missing_parameter (0.00s)
=== RUN   TestJsonRpc/complex,_parameter_not_matching
match ["==", ".jsonrpc.method", "debug_traceCall"] --> True
match ["==", ".jsonrpc.params[3]?", "callTracer"] --> False
match ["==", ".jsonrpc.params[3]?", "prestateTracer"] --> False
match ["or", [
  ["==", ".jsonrpc.params[3]?", "callTracer"],
  ["==", ".jsonrpc.params[3]?", "prestateTracer"]]]
 --> False
--- PASS: TestJsonRpc/complex,_parameter_not_matching (0.00s)
--- PASS: TestJsonRpc (0.00s)
PASS```