sp_BlitzFirst: add @ExpertMode = 2 switch to skip sp_BlitzWho

[BrentOzar]

Is your feature request related to a problem? Please describe.
Under extremely heavy load, I don't want to see sp_BlitzWho results when performance troubleshooting.

Describe the solution you'd like
For ExpertMode, add a 2 input that lets us skip sp_BlitzWho.

Describe alternatives you've considered
Adding another parameter to skip sp_BlitzWho output, but... I'd rather not add another parameter for this.

Are you ready to build the code for the feature?
Yep!