Add documentation for routes (#2496)

* Add documentation for routes

* Rename exit-node to routes and add redirects
* Add a new section on subnet routers
* Extend the existing exit-node documentation
* Describe auto approvers for subnet routers and exit nodes
* Provide ACL examples for subnet routers and exit nodes
* Describe HA and its current limitations
* Add a troubleshooting section with IP forwarding

* Update features page for 0.26

Add auto approvers and link to our documentation if available.

* Prefer the console lexer when commandline and output mixed

docs/setup/install/container.md

@@ -140,13 +140,13 @@ Additionally, the debug container includes a minimalist Busybox shell.
 
 To launch a shell in the container, use:
 
-```
+```shell
 docker run -it headscale/headscale:x.x.x-debug sh
 ```
 
 You can also execute commands directly, such as `ls /ko-app` in this example:
 
-```
+```shell
 docker run headscale/headscale:x.x.x-debug ls /ko-app
 ```