[Logging] debug_setVMLogTarget

Sets the output target of vmlog precompiled contract. When the output target is a file, logs from vmlog calls in smart contracts will be written to DATADIR/log/vm.log. Here DATADIR is the directory specified by --datadir when launching klay. On the other hand, the output target is stdout, logs will be displayed like a debug message on the standard output.

JSONRPC: debug_setVMLogTarget