Provide the ability to configure default subnet IDs via an argument or alternatively providing the ability to customize the discovery tag

[azagarelz]

What would you like to be added:
Provide an argument that allows specifying the subnet IDs to be used for pods instead of relying on the subnets autodiscovery.
Alternatively, providing the ability to customize the discovery tag would also work

Why is this needed:
Our current method of provisioning EKS clusters via Terraform automatically tags the required subnets.
Unfortunately, this also means that when a cluster is destroyed, those tags are removed.
Since the autodiscovery tag cannot be customized, all clusters using the same set of subnets rely on the same tags, and removing them breaks every cluster.
The autodiscovery looks like an advanced feature which seems unnecessary in most cases.