added sections and references in credentials handling in ECK

[eedugon]

This PR improves ECK managed credentials doc, with:

• Making it more complete, to look more similar to the original https://www.elastic.co/guide/en/cloud-on-k8s/2.16/k8s-users-and-roles.html
• Adding a link to that doc from the ECK Configure deployments landing page, otherwise it's not easy to find that document.
• Updated the example to use {{version.stack}} variable.

Preview

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy/cloud-on-k8s/configure-deployments.md
• deploy-manage/users-roles/cluster-or-deployment-auth/managed-credentials-eck.md

[eedugon]

We will add a comment and some references for external realms also, even if they are not handled by ECK features.

[shainaraskas]

couple small comments alongside linking to external realm docs :)

[barkbay]

LGTM

[barkbay]

I think I would mention the Kubernetes Secrets first. The reason is that being able to create users and roles in a declarative way is more aligned with how resources are managed in Kubernetes. I feel like manually interacting with a web ui is the last thing you want to do when you setup something in K8s (maybe I'm biased by all these years spent on Kubernetes 😄 ).

[eedugon]

Perfect, makes sense! I'll rephrase that a bit :)

I just took the same approach as in the original doc, but it's true that the original doc then provided all examples with secrets after the initial sentence.

[barkbay]

For the same reasons I would move this one before Native realm.

[eedugon]

@barkbay , review this whenever you have time, no rush. Besides the new content, try the links to see if the navigation experience makes sense (for file realm and custom roles mainly)

I know in the past we had all the content and examples in the same ECK-focused doc, but hopefully the current links still create a similar experience.

[barkbay]

LGTM 👍