openshift-install is creating user-defined tags (platform.aws.userTags) in subnets on AWS of BYO VPC (unmanaged VPC) deployment when using CAPA.

The documentation[1] for userTags state:
> A map of keys and values that the installation program adds as tags to all resources that it creates.

So when the network (VPC and subnets) are managed by user (BYO VPC), the installer should not create additional tags when provided in install-config.yaml. 

Investigating in CAPA codebase, the feature gate TagUnmanagedNetworkResources is enabled, and the subnet is propagating the userTags in the reconciliation loop[2].

[1] https://docs.openshift.com/container-platform/4.15/installing/installing_aws/installation-config-parameters-aws.html
[2] https://github.com/kubernetes-sigs/cluster-api-provider-aws/blob/main/pkg/cloud/services/network/subnets.go#L618

4.16.0-ec.6-x86_64

always

- 1. create VPC and subnets using CloudFormation. Example template: https://github.com/openshift/installer/blob/master/upi/aws/cloudformation/01_vpc.yaml
- 2. create install-config with user-tags and subnet IDs to install the cluster:
- 3. create the cluster with feature gate for CAPI 

```
featureSet: CustomNoUpgrade
featureGates:
- ClusterAPIInstall=true
metadata:
  name: "${CLUSTER_NAME}"
platform:
  aws:
    region: us-east-1
    subnets:
    - subnet-0165c70573a45651c
    - subnet-08540527fffeae3e9
    userTags:
      x-red-hat-clustertype: installer
      x-red-hat-managed: "true"
```

installer/CAPA is setting the user-defined tags in unmanaged subnets

- installer/CAPA does not create userTags on unmanaged subnets 
- userTags is applied for regular/standard workflow (managed VPC) with CAPA

- Impacting on SD/ROSA: https://redhat-internal.slack.com/archives/CCPBZPX7U/p1717588837289489