doc(self-managed): improve opensearch and irsa doc with placeholders and role mapping

[leiicamundi]

Description

This PR improves the IRSA instructions for Self-managed installation with the addition of placeholders and a missing instruction for OpenSearch.

it also introduces the alternative aws cli in tabs instead of terraform for user convenience

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.

[leiicamundi]

Note for the reviewer, I still need to test the commands with a real infra, otherwise the content and the form is ready to be review

[Langleu]

only reviewed the next docs, but left some smaller comments.
Overall, looks like a nice addition!

[christinaausley]

Is this in draft because there are additional changes coming, or is this ready for a final review? 😄

[leiicamundi]

Hello @christinaausley, after internal review, we will add additional things, I'll send you an update when it's ready to be reviewed.
Thank you

[Langleu]

Looks good from my side 👍, thanks for the adjustments 🚀

[leiicamundi]

I've double-checked the CLI commands, and everything is working.

@christinaausley, could you please perform a final review? After that, we'll be good to merge.

Thank you in advance!

[github-actions]

🧹 Preview environment for this PR has been torn down.

[leiicamundi]

@christinaausley The auto-merge feature merged the branch automatically—my mistake. Could you please review the changes and let me know if any further adjustments are needed? I've re-opened the branch.