sp_BlitzFirst: add parameter for which result sets to output

[BrentOzar]

Is your feature request related to a problem? Please describe.
Troubleshooting a server under high concurrency, and we don't want to bother seeing output result sets that aren't relevant to the problem at hand.

Describe the solution you'd like
New parameter for OutputResultSets, nvarchar(2000), default value: BlitzWho_Start|Findings|FileStats|PerfmonStats|WaitStats|BlitzCache|BlitzWho_End

If people don't want one or more of the result sets, they comment it out. Then in the script, as each set would be run, we check that string looking for LIKE %BlitzWho_Start%' so that way we don't have to parse the string or do comma delimited stuff. No, they won't be able to reorder the output.

Are you ready to build the code for the feature?
Yes.