docs: Move router tutorial (toh) from router.md to new file (#37979)

In an effort to make angular documentation easier for users to read,
we are moving the router tutorial currently in router.md to a new file.
To support this change, we have done the following:

* Update files to fix any broken links caused by moving the file
* Updated the new file to follow tutorial guidelines
* Add the new file to the table of  contents under, Tutorials.

PR Close #37979

packages/router/src/events.ts

@@ -127,7 +127,7 @@ export class NavigationEnd extends RouterEvent {
 /**
  * An event triggered when a navigation is canceled, directly or indirectly.
  *
- * This can happen when a [route guard](guide/router#milestone-5-route-guards)
+ * This can happen when a [route guard](guide/router-tutorial-toh#milestone-5-route-guards)
  * returns `false` or initiates a redirect by returning a `UrlTree`.
  *
  * @publicApi