feat(self-managed): OpenShift ROSA instructions and rework of the reference arch for OpenShift

[leiicamundi]

Description

This PR revises the installation instructions for Camunda 8 on OpenShift, taking into account versions 8.7 and 8.6.

• For version 8.7, the instructions are functional, but the installation process is still broken. This will be fixed during the QA process.
• This update also adds a reference to the installation of a ROSA cluster.
• Additionally, the instructions for installing Camunda 8 on an OpenShift cluster have been reworked to include routes as the default exposure solution.
• Similar to doc(self-managed): add infrastructure diagrams for EKS #4714, we add diagrams

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]

👋 🤖 ✅ Looks like the changes were ported across versions, nice job! 🎉

You can read more about the versioning within our docs in our documentation guidelines.

[conceptualshark]

Made some small copy edits and left a non-blocking suggestion - I love the reusable structure of these guides, makes the content much easier to read and review!

[Langleu]

Some smaller requests, I only reviewed the next part and would assume 8.6 is the same.

Overall looks quite good 🚀.
I did not try to follow it step by step, let me know if I should run through it all.

[Langleu]

Thanks for the quick adjustments, the only thing I'd probably change is the AWS CLI recommendation still

[conceptualshark]

Made a few grammar edits and left a small comment regarding wording but otherwise this looks to be in a good place to me. Approving regardless, just let me know if anything else gets updated and this needs a final thumbs up. 👍

[github-actions]

The preview environment relating to the commit e79b6a4 has successfully been deployed. You can access it at https://preview.docs.camunda.cloud/pr-4734/index.html