[backport v2.8-Next2][BUG] Rancher Backups not persisting installed UI extensions

[github-actions[bot]]

This is a backport issue for #483, automatically created via GitHub Actions workflow initiated by @mallardduck

Original issue body:

Rancher Server Setup

• Rancher version: Any
• Kubernetes Version and Engine: N/A

Describe the bug When using BRO to migrate Rancher to a new cluster the UI extensions do not persist. This is because the CRD responsible for UI plugins are not being backed up. Those are uiplugins.catalog.cattle.io and seem to be under cattle-ui-plugin-system namespace.

To Reproduce Steps to reproduce the behavior:

1. Install a Rancher UI plugin,
2. Take a backup,
3. Migrate to a new cluster,
4. Observe the UI plugin is not active/installed.

Expected behavior I believe we can expect these to be installed after a migration. However we will want to work with UI team (anyone more expert on UI plugins than us) to understand this. For instance, if UI plugins/extensions must be installed via clicking the UI buttons and applying CRDs won't work.

Note: For more context, we got word of the CRD needed via a slack thread (must be SUSE employee to see). Might be useful for other SME to reach out to.

[nickwsuse]

Verified on v2.8-head ID: 68e5d43 and Rancher Backups v103.0.3+up4.0.3 ✅

All checks completed on fresh installs and upgrades from 2.8.7 -> 2.8-head

• Rancher Backups resource set shows updates to include resources from the cattle-ui-plugin-system namespace ✅
• UI Plugin resources still in place after in-place restore ✅
• UI Plugin resources still in place after rollback on the same server ✅
• UI Plugin resources still in place after migration from one cluster to a new one ✅