MGMT-20246: Implement UI for custom manifests

[jgyselov]

📝 Summary

Ticket Summary (Title):
Implement UI for custom manifests

Ticket Link:
https://issues.redhat.com/browse/MGMT-20246

AI Lib PR: openshift-assisted/assisted-installer-ui#2942

Type of Change:

• 🐞 Bug Fix
• ✨ Feature
• 🔧 Refactor
• 💸 Tech Debt
• 🧪 Test-related
• 📄 Docs

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✅ Checklist

General

• PR title follows the convention (e.g. ACM-12340 Fix bug with...)
• Code builds and runs locally without errors
• No console logs, commented-out code, or unnecessary files
• All commits are meaningful and well-labeled
• All new display strings are externalized for localization (English only)
• (Nice to have) JSDoc comments added for new functions and interfaces

If Feature

• UI/UX reviewed (if applicable)
• All acceptance criteria met
• Unit test coverage added or updated
• Relevant documentation or comments included

If Bugfix

• Root cause and fix summary are documented in the ticket (for future reference / errata)
• Fix tested thoroughly and resolves the issue
• Test(s) added to prevent regression

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🗒️ Notes for Reviewers

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: jgyselov
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[openshift-ci]

@jgyselov: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/check	1a25d30	link	true	/test check
ci/prow/unit-tests-sonarcloud	1a25d30	link	true	/test unit-tests-sonarcloud

Full PR test history. Your PR dashboard.

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