User Story:

As a (user persona), I want to be able to SSH into a bastion host (if enabled) over IPv6 when the cluster is IPv6-enabled.

Currently, the bastion security group (SG) is only configured to allow IPv4 CIDRs.

Acceptance Criteria:

Description of criteria:

• Allowed IPv6 CIDRs for bastion SSH should be configurable.
• Allowed IPv6 CIDRs for bastion SSH should default to ::/0 if unset.
• Allowed IPv6 CIDRs for bastion SSH should be added to bastion SG.

(optional) Out of Scope:

Detail about what is specifically not being delivered in the story

Engineering Details:

• Bastion type definition: https://github.com/kubernetes-sigs/cluster-api-provider-aws/blob/517ae6c7662baa564b37b48c1d38de8d4aac991f/api/v1beta2/awscluster_types.go#L156
• Bastion SG configuration: https://github.com/kubernetes-sigs/cluster-api-provider-aws/blob/4e912b4e4d1f855abf9b5194acaf9f31b5763c57/pkg/cloud/services/securitygroup/securitygroups.go#L596-L604
• We can either define a new field or extend the existing one awscluster.spec.bastion.allowedCIDRBlocks to accept IPv6 CIDRs.

This requires/does not require a design proposal.
This requires/does not require a feature gate.