codeowner: Add owners for examples in network category

New example folder `network` has been introduced in 4ac24549ad to
hold examples related to generic networking, not specifically to
ethernet nor wifi. This change however didn't assign code owners, so
only IDF maintainers could approve MRs.

Assigning code ownership to groups:
* network
* wifi

.gitlab/CODEOWNERS

@@ -161,6 +161,7 @@
 /examples/ethernet/           @esp-idf-codeowners/network
 /examples/get-started/        @esp-idf-codeowners/system
 /examples/mesh/               @esp-idf-codeowners/wifi
+/examples/network/            @esp-idf-codeowners/network @esp-idf-codeowners/wifi
 /examples/openthread/         @esp-idf-codeowners/ieee802154
 /examples/peripherals/        @esp-idf-codeowners/peripherals
 /examples/protocols/          @esp-idf-codeowners/network @esp-idf-codeowners/app-utilities