[DirectX] Add @bogner as DX backend maintainer (#114872)

@bogner has a long history with the LLVM community as a contributor and
maintainer of a wide array of project areas. He is providing a lot of
the leadership and direction for the contributors working on the DirectX
backend, and should be recognized as its maintainer.

Author: llvm-beanz

llvm/Maintainers.md

@@ -179,6 +179,11 @@ [email protected] (email), [4ast](https://github.com/4ast) (GitHub)
 Zi Xuan Wu (Zeson) \
 [email protected] (email), [zixuan-wu](https://github.com/zixuan-wu) (GitHub)
 
+#### DirectX backend
+
+Justin Bogner \
+[email protected] (email), [bogner](https://github.com/bogner) (GitHub)
+
 #### Hexagon backend
 
 Sundeep Kushwaha \