[EKS] [request]: EKS Capability ArgoCD Custom URL

### Community Note

* Please vote on this issue by adding a 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to the original issue to help the community and maintainers prioritize this request
* Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request
* If you are interested in working on this issue or have submitted a pull request, please leave a comment

**Tell us about your request**
Enable EKS Capability URL to be customized via CNAME in Route53

**Which service(s) is this request for?**
EKS,

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
When an EKS ArgoCD Capability is created, an endpoint url of this format is generated:
**[some_aws_string].eks-capabilities.[region].amazonaws.com**

This isn't a very friendly format for users, so I tried creating a CNAME and pointing to that endpoint, this fails to work with a 404 Error.
The reason is like in Self Managed ArgoCD you'd place it behind an Ingress and a ELB for access which takes care of headers passing through.
When using the Capability URL and CNAME, that header transformation that ELB/Ingress can do, is missing thus making it impossible to use a custom URL.

**Are you currently working around this issue?**
Its a limitation confimed by AWS Service team.

**Additional context**
None.

**Attachments**
None.