[SYCL][CODEOWNERS] Update CODEOWNERS for SYCL-Graph extension (#10155)

Have @intel/sycl-graphs-reviewers with members:

* Ewan Crawford @EwanC - Codeplay
* Ben Tracy @Bensuo - Codeplay 
* Maxime France-Pillois @mfrancepillois - Codeplay
* Pablo Reble @reble - Intel
* Julian Miller @julianmi - Intel
* Stewart Dale @stdale-intel - Intel

As reviewers for the following files relating to the implementation of
the [experimental SYCL-Graph
extension]:(#5626)
*
[sycl/include/sycl/ext/oneapi/experimental/graph.hpp](https://github.com/intel/llvm/blob/sycl/sycl/include/sycl/ext/oneapi/experimental/graph.hpp)
*
[sycl/source/detail/graph_impl.cpp](https://github.com/intel/llvm/blob/sycl/sycl/source/detail/graph_impl.cpp)
*
[sycl/source/detail/graph_impl.hpp](https://github.com/intel/llvm/blob/sycl/sycl/source/detail/graph_impl.hpp)
*
[sycl/unittests/Extensions/CommandGraph.cpp](https://github.com/intel/llvm/blob/sycl/sycl/unittests/Extensions/CommandGraph.cpp)

Author: EwanC

.github/CODEOWNERS

@@ -114,3 +114,9 @@ clang/test/Driver/sycl-native-cpu*.cpp @intel/dpcpp-nativecpu-pi-reviewers
 sycl/**/native_cpu/ @intel/dpcpp-nativecpu-pi-reviewers
 sycl/doc/design/SYCLNativeCPU.md @intel/dpcpp-nativecpu-pi-reviewers
 sycl/include/sycl/detail/native_cpu.hpp @intel/dpcpp-nativecpu-pi-reviewers
+
+# SYCL-Graphs extensions
+sycl/include/sycl/ext/oneapi/experimental/graph.hpp @intel/sycl-graphs-reviewers
+sycl/source/detail/graph_impl.cpp @intel/sycl-graphs-reviewers
+sycl/source/detail/graph_impl.hpp @intel/sycl-graphs-reviewers
+sycl/unittests/Extensions/CommandGraph.cpp @intel/sycl-graphs-reviewers