Include trace and span identifier in decision logs

Currently OPA's decision logs do not include the trace
and span identifier associated with a given request
handled by the server. This information if available
can be helpful to correlate logs and trace data.

This change updates the decision log format to now
include the trace and span identifier if present.

Fixes: #5230

Signed-off-by: Ashutosh Narkar <anarkar4387@gmail.com>