Add documentation about route table quota limits with regards to overlay free networking

[ScheererJ]

How to categorize this issue?

/area documentation
/area networking
/kind enhancement
/platform aws

What would you like to be added:
Add documentation about route table quota limits with regards to overlay free networking.

Why is this needed:
In case the overlay network is disabled, the routes required by the pod network are configured in the virtual network (VPC). The aws-custom-route-controller performs this if required.

Unfortunately, the default quotas for route table entries per route table are fairly limited with only 50 entries. This means that a cluster more than 50 nodes will run into the default limit resulting in a partially unusable pod network.

Apart from the default limit (50) it is also important to mention the hard limit of 1000 route table entries resulting in a hard stop regarding the amount of cluster nodes that can be used in an overlay free pod network.