Update clr-configuration-knobs.md, add new C# csi.exe based script for xplat documen...

 Update clr-configuration-knobs.md, add new C# csi.exe based script for xplat document generation (#15858)

* C# csx script to generate CoreCLR and Jit configuration knobs doc

* Normalize category names, fix typos and white space in clrconfigvalues.h

* Normalize category names, knobs descrptions and fix typos in jitconfigvalues.h

* Remove clr-complus-conf-docgen.sh

* Remove from clrconfigvalues.h CONFIG_ declarations which are already present in jitconfigvalues.h

* Update clr-configuration-knobs.md with clr-configuration-knobs.csx script