Enable IMDS IPv6 endpoint

This is unconditionally enabled.
There is an IPv4-equivlanet "HttpEndpoint" field [0] that defaults to enabled and we dont expose a way to disable it.
HttpProtocolIpv6 defaults to disabled, so to have it match the same behavior of HttpEndpoint we hardcode it to enabled.
Since we dont allow the ipv4 endpoint to be disabled, I dont think we need to expose a new API field to allow this to be overridden either.

I chose not to expose it through the model since any kops upgrade to include this functionality will always have other LaunchTemplate changes that will prompt a new LT version to be written which will include this change, so we dont need to find and detect any necessary LT updates for this field.

[0] https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_LaunchTemplateInstanceMetadataOptions.html#API_LaunchTemplateInstanceMetadataOptions_Contents

upup/pkg/fi/cloudup/awstasks/launchtemplate_target_api.go

@@ -45,6 +45,7 @@ func (t *LaunchTemplate) RenderAWS(c *awsup.AWSAPITarget, a, e, changes *LaunchT
 		MetadataOptions: &ec2.LaunchTemplateInstanceMetadataOptionsRequest{
 			HttpPutResponseHopLimit: t.HTTPPutResponseHopLimit,
 			HttpTokens:              t.HTTPTokens,
+			HttpProtocolIpv6:        aws.String(ec2.LaunchTemplateInstanceMetadataProtocolIpv6Enabled),
 		},
 		NetworkInterfaces: []*ec2.LaunchTemplateInstanceNetworkInterfaceSpecificationRequest{
 			{