Bug 1989504: Do not require override when clearing unkown channel

Add more detailed information to help info and output messages. And
make a change to not require --allow-explicit-channel when clearing
an unkown channel. More info is in this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1989504

pkg/cli/admin/upgrade/channel/channel.go

@@ -32,8 +32,13 @@ func New(f kcmdutil.Factory, streams genericclioptions.IOStreams) *cobra.Command
 			This command will set or clear the update channel, which impacts the list of updates
 			recommended for the cluster.
 
-			If there is a list of acceptable channels and the desired channel is not in that list,
-			you must pass --allow-explicit-channel to allow channel change to proceed.
+			If desired channel is empty, the command will clear the update channel. If there is a list of
+			acceptable channels and the current update channel is in that list, you must pass --allow-explicit-channel to allow channel clear to
+			proceed.
+
+			If desired channel is not empty, the command will set the update channel to it. If there is a list of
+			acceptable channels and the desired channel is not in that list, you must pass --allow-explicit-channel
+			to allow channel change to proceed.
 		`),
 		Run: func(cmd *cobra.Command, args []string) {
 			kcmdutil.CheckErr(o.Complete(f, cmd, args))
@@ -86,31 +91,38 @@ func (o *Options) Run() error {
 
 	if o.Channel == cv.Spec.Channel {
 		if cv.Spec.Channel == "" {
-			fmt.Fprint(o.Out, "info: Cluster channel is already clear\n")
+			fmt.Fprint(o.Out, "info: Cluster channel is already clear (no change)\n")
 		} else {
-			fmt.Fprintf(o.Out, "info: Cluster is already in %s\n", cv.Spec.Channel)
+			fmt.Fprintf(o.Out, "info: Cluster is already in %s (no change)\n", cv.Spec.Channel)
 		}
 		return nil
 	}
 
 	if len(cv.Status.Desired.Channels) > 0 {
-		found := false
+		found, known := false, false
 		for _, channel := range cv.Status.Desired.Channels {
 			if channel == o.Channel {
 				found = true
+			}
+			if channel == cv.Spec.Channel {
+				known = true
+			}
+			if found && known {
 				break
 			}
 		}
-		if !found {
+		if o.Channel == "" {
+			if known && !o.AllowExplicitChannel {
+				return fmt.Errorf("You are requesting to clear the update channel. The current channel %q is one of the available channels, you must pass --allow-explicit-channel to continue\n", cv.Spec.Channel)
+			}
+		} else if !found {
 			if !o.AllowExplicitChannel {
 				return fmt.Errorf("the requested channel %q is not one of the available channels (%s), you must pass --allow-explicit-channel to continue\n", o.Channel, strings.Join(cv.Status.Desired.Channels, ", "))
 			}
-			if o.Channel != "" {
-				fmt.Fprintf(o.ErrOut, "warning: The requested channel %q is not one of the available channels (%s).  You have used --allow-explicit-channel to proceed anyway.\n", o.Channel, strings.Join(cv.Status.Desired.Channels, ", "))
-			}
+			fmt.Fprintf(o.ErrOut, "warning: The requested channel %q is not one of the available channels (%s). You have used --allow-explicit-channel to proceed anyway. Setting the update channel to %q.\n", o.Channel, strings.Join(cv.Status.Desired.Channels, ", "), o.Channel)
 		}
 	} else if o.Channel != "" {
-		fmt.Fprintf(o.ErrOut, "warning: No channels known to be compatible with the current version %q; unable to validate %q.\n", cv.Status.Desired.Version, o.Channel)
+		fmt.Fprintf(o.ErrOut, "warning: No channels known to be compatible with the current version %q; unable to validate %q. Setting the update channel to %q anyway.\n", cv.Status.Desired.Version, o.Channel, o.Channel)
 	}
 
 	if o.Channel == "" {