update version of ingress-nginx controller in docs. (#6855)

* update version of ingress-nginx controller.

Change tag from controller-v0.34.0 to controller-v0.40.2 to use newest tag.

* Update docs about aws deploy templates.

In the yaml templates, there is no mention of idle timeouts. This is why I removed the documentation about it. This might be a mistake. Please verify this. I don't know enough to verify it myself.

* Change label when checking version.

When checking for `app.kubernetes.io/name=ingress-nginx`, a completed pod was selected which is not helpful when trying to `exec`. Changing the label selects the running controller pod.

* put back the information about ELB Idle Timeouts.

When I removed the information, I had overlooked that it was mentioned in the L7 yaml file. Thanks.