Better doc for channel config via operator (#2990)

* 💄 Adding a bit of more context to the different options for a 'default channel'

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* Fixing comments

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* Updating to use lower-case, like the rest of the doc does

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* Adding IMC as an alternative channel for configures

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* Update docs/install/operator/configuring-eventing-cr.md

Co-authored-by: Mike Petersen <mpetason@gmail.com>

* Update docs/install/operator/configuring-eventing-cr.md

Co-authored-by: Mike Petersen <mpetason@gmail.com>

Co-authored-by: Mike Petersen <mpetason@gmail.com>

docs/install/operator/configuring-eventing-cr.md

@@ -47,11 +47,46 @@ if the current Knative Eventing deployment is version 0.14.x, you must upgrade t
 The Knative Eventing operator CR is configured the same way as the Knative Serving operator CR. Because the operator manages
 the Knative Eventing installation, it will overwrite any updates to the `ConfigMaps` which are used to configure Knative
 Eventing. The `KnativeEventing` custom resource allows you to set values for these ConfigMaps via the operator. Knative
-Eventing has multiple ConfigMaps named with the prefix `config-`. The `spec.config` in `KnativeEventing` has one entry
+Eventing has multiple ConfigMaps, most of them are named with the prefix `config-`. The `spec.config` in `KnativeEventing` has one entry
 `<name>` for each ConfigMap named `config-<name>`, with a value which will be used for the ConfigMap's `data`.
 
+### Setting the default channel
+
 For example, if you would like to change your default channel from `InMemoryChannel` into `KafkaChannel`, here is what
-your Eventing CR looks like, to modify the ConfigMap `config-br-default-channel`:
+your Eventing CR looks like, to modify the ConfigMap `default-ch-webhook`:
+
+```
+apiVersion: operator.knative.dev/v1alpha1
+kind: KnativeEventing
+metadata:
+  name: knative-eventing
+  namespace: knative-eventing
+spec:
+  config:
+    default-ch-webhook:
+      default-ch-config: |
+        clusterDefault:
+          apiVersion: messaging.knative.dev/v1beta1
+          kind: KafkaChannel
+          spec:
+            numPartitions: 10
+            replicationFactor: 1
+        namespaceDefaults:
+          my-namespace:
+            apiVersion: messaging.knative.dev/v1
+            kind: InMemoryChannel
+            spec:
+              delivery:
+                backoffDelay: PT0.5S
+                backoffPolicy: exponential
+                retry: 5
+```
+
+The `clusterDefault` sets the global, cluster based default. Inside the `namespaceDefaults` you can configure the channel defaults on a per namespace basis.
+
+### Setting the default channel for the broker
+
+If you are using a channel-based broker and you would like to change the brokers default channel, from `InMemoryChannel` to `KafkaChannel`, here is an example of what your Eventing CR would look like when modifying the ConfigMap `config-br-default-channel`:
 
 ```
 apiVersion: operator.knative.dev/v1alpha1
@@ -66,7 +101,7 @@ spec:
         apiVersion: messaging.knative.dev/v1beta1
         kind: KafkaChannel
         spec:
-          numPartitions: 10
+          numPartitions: 5
           replicationFactor: 1
 ```