Update error message for missing application (#6281)

# Description

Adds an additional error message to `rad resource list`.

## Type of change

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Fixes: #6236

## Auto-generated summary

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copilot:all
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### <samp>🤖 Generated by Copilot at 4cbfd98</samp>

### Summary
🧪📝🚀

<!--
1.  🧪 for updating the test case
2.  📝 for adding a more helpful error message
3.  🚀 for improving the user experience of the CLI
-->
Improve error handling and testing for `resource list` command. Add a
clearer error message for invalid applications and update the
corresponding test case.

> _`Run` test updated_
> _Error message more helpful_
> _Autumn of bug fixes_

### Walkthrough
* Improve error message for invalid application name in `list` command
([link](https://github.com/radius-project/radius/pull/6281/files?diff=unified&w=0#diff-b21dcd67dbc0d24e0f8bba90701dfcfb5736cf40427547c7a7ccb91478f262cfL160-R160))
* Update test case for `Run` function in `list_test.go` to match new
error message
([link](https://github.com/radius-project/radius/pull/6281/files?diff=unified&w=0#diff-d57c4c1535dd3783fc94937211b66a786a621683678bcefdef775626c9e22c5eL125-R125))

pkg/cli/cmd/resource/list/list.go

@@ -157,7 +157,7 @@ func (r *Runner) Run(ctx context.Context) error {
 	} else {
 		_, err = client.ShowApplication(ctx, r.ApplicationName)
 		if clients.Is404Error(err) {
-			return clierrors.Message("The application %q could not be found in workspace %q.", r.ApplicationName, r.Workspace.Name)
+			return clierrors.Message("The application %q could not be found in workspace %q. Make sure you specify the correct application with '-a/--application' or switch applications with 'rad app switch'.", r.ApplicationName, r.Workspace.Name)
 		} else if err != nil {
 			return err
 		}

pkg/cli/cmd/resource/list/list_test.go

@@ -122,7 +122,7 @@ func Test_Run(t *testing.T) {
 
 			err := runner.Run(context.Background())
 			require.Error(t, err)
-			require.IsType(t, err, clierrors.Message("The application %q could not be found in workspace %q.", "test-app", radcli.TestWorkspaceName))
+			require.IsType(t, err, clierrors.Message("The application %q could not be found in workspace %q. Make sure you specify the correct application with '-a/--application' or switch applications with 'rad app switch'.", "test-app", radcli.TestWorkspaceName))
 		})
 
 		t.Run("Success", func(t *testing.T) {