Add sig-network-service-apis slack channel. (#4281)

Adds the sig-network-service-apis slack channel.
As this is the first time, also adds OWNERS file
to the sig-network/ directory.

communication/slack-config/restrictions.yaml

@@ -19,6 +19,9 @@ restrictions:
       - "^release-"
     usergroups:
       - "^release-"
+  - path: "sig-network/*.yaml"
+    channels:
+      - "^sig-network-.*$"
   - path: "sig-storage/*.yaml"
     channels:
       - "^sig-storage$"

communication/slack-config/sig-network/OWNERS

@@ -0,0 +1,7 @@
+# See the OWNERS docs at https://go.k8s.io/owners
+reviewers:
+  - sig-network-leads
+approvers:
+  - sig-network-leads
+labels:
+  - sig/network

communication/slack-config/sig-network/config.yaml

@@ -0,0 +1,2 @@
+channels:
+  - name: sig-network-service-apis