Support for idmapped mounts instead of shiftfs

Is your feature request related to a problem? Please describe

We may have a chance to use idmapped mounts instead of shifts. idmapped has the merit that it doesn't need to kernel module because this feature is included kernel since >= 5.12. I'm not sure the performance, but at least it's better than fuse.
https://github.com/lxc/lxd/pull/8778/files

And, it may help the self-hosted users because the users use it easily, and don't need to install fuse-overlayfs or kernel module.

Describe the behaviour you'd like

1. Pass the integration test with idmapped mounts, with fuse, shiftfs, and id mapped mounts.
   • Update harvestor preview environments to use ID mapped mounts
   • workspace-preview changed to id-mapped and tested
   • Production (ops repo) changed to id-mapped and tested with an ephemeral cluster
2. Share thoughts on how to automate testing with fuse and shiftfs in a new (separate issue), as the current tests will only use what is in the preview environment.
3. Update the product compatibility matrix (internal)

Describe alternatives you've considered

Additional context

Internal conversation

Start with the integration test and the linked LXD pull request to understand the requested idmapped-mount behavior alongside fuse and shiftfs. Done means updating the harvestor preview environment and workspace-preview, validating production with an ephemeral cluster, documenting separate-test automation thoughts in a new issue, and updating the internal compatibility matrix.