[EKS Capabilities] [request]: Expose argocd-webhook-creds-secret configuration

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**Tell us about your request**
What do you want us to build?

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
The secret to put Github webhook secret is I think automatically created when ArgoCD Capability is enabled e.g.:
```
apiVersion: v1
data:
webhook.azuredevops.password: ""
webhook.azuredevops.username: ""
webhook.bitbucket.uuid: ""
webhook.bitbucketserver.secret: ""
webhook.github.secret: ""
webhook.gitlab.secret: ""
webhook.gogs.secret: ""
kind: Secret
metadata:
creationTimestamp: "2026-08-20T08:46:08Z"
labels:
argocd.argoproj.io/secret-type: webhook
name: argocd-webhook-creds-secret
namespace: argocd
resourceVersion: "555756101"
uid: 1ef7c836-fefe-43c6-ab11-faf436f7ba4e
type: Opaque
```
should I just own/overwrite it with the actual secret value? or what other mechanism there is to tell ArgoCD Capability to use a particular value?
I went through: https://docs.aws.amazon.com/eks/latest/userguide/argocd-configure-repositories.html
but there's no mention of webhook Secret.

**Are you currently working around this issue?**
Polling works ofc, or manual refresh/sync.

**Additional context**
Anything else we should know?

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

Start with the linked EKS documentation for configuring Argo CD repositories and compare it with the generated argocd-webhook-creds-secret shown in the issue. Determine the supported configuration path for a GitHub webhook secret; done means users can provide a specific value and the behavior is documented.

Written by the indexing model from the issue text.