Set process valheim_server.exe with high priority on start

[mockdot]

I am not completely sure how beneficial this really is, I have read suggestions and it feels (not sure if it's a placebo effect) as if the server ran a little smoother when manually setting the process to high priority rather than normal.

[Razzmatazzz]

I might add it as an option, but the MS docs warn against it:

Use extreme care when specifying High for the process's priority class, because a high priority class application can use nearly all available processor time.

[Razzmatazzz]

Added in latest release.