chore: add Doxyfile to the DefaultInfo files

doxygen/doxygen.bzl

diff --git a/doxygen/doxygen.bzl b/doxygen/doxygen.bzl
index fcf676e..f75bd29 100644
--- a/doxygen/doxygen.bzl
+++ b/doxygen/doxygen.bzl
@@ -88,7 +88,7 @@
     )
 
     return [
-        DefaultInfo(files = depset(outs)),
+        DefaultInfo(files = depset(outs + [doxyfile])),
         OutputGroupInfo(**output_group_info),
     ]