Rename intel_reqd_group_size metadata

[smanna12]

I suppose intel_reqd_group_size will also be renamed? In a separate patch maybe?

intel_reqd_group_size is not new to the optional device features design so the renaming should happen separately.

Originally posted by @steffenlarsen in https://github.com/intel/llvm/issues/6822#issuecomment-1252444481