message: [docs] Add doxygen to path in build
  The documentation build was failing because it could not find the doxygen
  executable.
  Add doxygen path to `$env:PATH` in build script. Add some messages to debug
  failures that might happen in future.
  Fixes
diff: $env:Path = "$machinePath;$userPath"
  + $env:Path += "C:\Program Files\doxygen\bin"
  +
  + Get-Command doxygen,pandoc
  +
  }
  if (($env:BOND_BUILD -eq 'C++') -and (-not ($env:BOND_CMAKE_FLAGS -match '-DBOND_ENABLE_GRPC=FALSE'))) {
  