[DirectX][obcopy] Add support for `--add-section` for DXContainer

[llvm-beanz]

--add-section is a useful way to implement some of the other features that we need for DX container manipulation, so we should add it when we get around to it.

[llvmbot]

@llvm/issue-subscribers-tools-llvm-objcopy-strip

Author: Chris B (llvm-beanz)

`--add-section` is a useful way to implement some of the other features that we need for DX container manipulation, so we should add it when we get around to it.