Adding setting default channel to yaml based install (#4263)

* adding setting default channel to yaml install

* adding section into admin guide for channel defaults

* removing trailing whitespaces

* EOF new line

* applying suggestions

* Update docs/admin/eventing/channel-configuration.md

* adding more details

* applying suggestions, adding link and removing dup

* linting

Co-authored-by: Ashleigh Brennan <abrennan@redhat.com>

config/nav.yml

@@ -58,6 +58,7 @@ nav:
           - Configure the Defaults ConfigMap: admin/serving/config-defaults.md
         # Eventing config
         - Knative Eventing configuration:
+          - Configure Channel defaults: admin/eventing/channel-configuration.md
           - Configure Broker defaults: admin/eventing/broker-configuration.md
           - Configure Kafka Channel defaults: admin/eventing/kafka-channel-configuration.md
           - Configure event source defaults: admin/eventing/sources-configuration.md

docs/admin/eventing/channel-configuration.md

@@ -0,0 +1,33 @@
+# Configure Channel defaults
+
+Knative Eventing provides a `default-ch-webhook` ConfigMap that contains the configuration settings that govern default Channel creation.
+
+The default `default-ch-webhook` ConfigMap is as follows:
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: default-ch-webhook
+  namespace: knative-eventing
+  labels:
+    eventing.knative.dev/release: devel
+    app.kubernetes.io/version: devel
+    app.kubernetes.io/part-of: knative-eventing
+data:
+  default-ch-config: |
+    clusterDefault:
+      apiVersion: messaging.knative.dev/v1
+      kind: InMemoryChannel
+    namespaceDefaults:
+      some-namespace:
+        apiVersion: messaging.knative.dev/v1
+        kind: InMemoryChannel
+```
+
+By changing the `data.default-ch-config` property we can define the clusterDefaults and per Namespace defaults.
+
+This configuration is used by the Channel custom resource definition (CRD) to create platform specific implementations. 
+
+!!! note
+  The `clusterDefault` setting determines the global, cluster-wide default Channel type. You can configure Channel defaults for individual namespaces by using the `namespaceDefaults` setting.

docs/admin/install/eventing/install-eventing-with-yaml.md

@@ -90,6 +90,8 @@ Follow the procedure for the Channel of your choice:
 
         <!-- TODO(https://github.com/knative/docs/issues/2153): Add more Channels here -->
 
+You can change the default channel implementation by following the instructions described in the [Configure Channel defaults](../../eventing/channel-configuration.md) section.
+
 ## Optional: Install a Broker layer:
 
 The following tabs expand to show instructions for installing the Broker layer.