doc(self-managed): add infrastructure diagrams for EKS

[leiicamundi]

Description

This PR introduces reference architecture diagrams following the effort referenced in https://github.com/camunda/team-infrastructure-experience/issues/498. This PR is currently focused on EKS only as ROSA will have a dedicated PR.

The diagrams are only applicable to 8.7 as we don't plan to backport it to previous versions.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[github-actions]

👋 🤖 🤔 Hello, @leiicamundi! Did you make your changes in all the right places?

These files were changed only in docs/. You might want to duplicate these changes in versioned_docs/version-8.6/.

• docs/self-managed/setup/deploy/amazon/amazon-eks/assets/eks-dual-region.jpg
• docs/self-managed/setup/deploy/amazon/amazon-eks/assets/eks-dual-region.pdf
• docs/self-managed/setup/deploy/amazon/amazon-eks/assets/eks-single-region.jpg
• docs/self-managed/setup/deploy/amazon/amazon-eks/assets/eks-single-region.pdf
• docs/self-managed/setup/deploy/amazon/amazon-eks/dual-region.md
• docs/self-managed/setup/deploy/amazon/amazon-eks/terraform-setup.md

You may have done this intentionally, but we wanted to point it out in case you didn't. You can read more about the versioning within our docs in our documentation guidelines.

[conceptualshark]

These diagrams look great to me, and I like the inclusion of the full-size links. Happy to approve, but will defer to @mesellings if there are any suggestions on how to best direct a user to click the image.

[mesellings]

@leiicamundi As mentioned I can take a look at this after the release next week, but as part of the release announcements I edited the Miro diagrams in #4715, so you can see the type of work I was talking about, i.e. to get the Miro diagrams into shape for the docs.

e.g.