🌱 ETCD backup/restore: use structured setting

[Danil-Grigorev]

What this PR does / why we need it:

ADR 0009 established usage of structured proxy types in turtles. Currently, there is a usage of unstructured in etcdbackup/restore package. This change moves internal rancher package to public api, allowing to import existing API types.

This change is a result of a previous discussion https://github.com/rancher/turtles/pull/542#discussion_r1627644490 and a followup request https://github.com/rancher/turtles/pull/542#pullrequestreview-2191613825

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Special notes for your reviewer:

Checklist:

• [ ] squashed commits into logical changes
• [ ] includes documentation
• [ ] adds unit tests
• [ ] adds or updates e2e tests