feat: add external property to coder_app (#5425)

* Add schema

* feat: add `external` property to `coder_app`

This allows exposing applications that open an external URL.

coderd/workspaceagents.go

@@ -644,6 +644,8 @@ func convertApps(dbApps []database.WorkspaceApp) []codersdk.WorkspaceApp {
 	for _, dbApp := range dbApps {
 		apps = append(apps, codersdk.WorkspaceApp{
 			ID:           dbApp.ID,
+			URL:          dbApp.Url.String,
+			External:     dbApp.External,
 			Slug:         dbApp.Slug,
 			DisplayName:  dbApp.DisplayName,
 			Command:      dbApp.Command.String,