process-level metrics for win_stat input plugin

**Is your feature request related to a problem? Please describe.**
The proc and cpu input plugins for linux allow a process name/pid to be specified to be able to get memory and cpu usage stats. There is no equivalent to this for windows.

**Describe the solution you'd like**
Allow a parameter to specify a process for the win_stat plugin to get cpu and memory stats for the specific process.

**Additional context**
We are using proc and cpu input plugins to monitor usage for specific processes for linux but would like an equivalent for our windows workloads.