CAPA route table reconciliation should add missing routes (and not only fix mismatches)

[AndiDog]

Chat ref.

This was a case of a prepared VPC which CAPA was supposed to take over. There was no 0.0.0.0/0 route, but since that destination is in the desired routes (see function getRoutesToPrivateSubnet), it should be reconciled i.e. added. Right now, CAPA only fixes routes whose destination CIDR matches between desired/actual if other fields mismatch. It does not do full reconciliation.

[AndiDog]

Upstream fix just created: kubernetes-sigs/cluster-api-provider-aws#6047. We can consider placing this in the fork as backport, once well-tested and only if we think the fix can't wait.