Move Klio's Kopia fork from leonardoce/kopia to cloudnative-pg/kopia

We're moving the fork of Kopia that Klio builds against under the `cloudnative-pg` org, so it's maintained as part of the project.

What's been done

- Forked `kopia/kopia` into `cloudnative-pg/kopia`.
- Created a `klio` branch on the new fork, starting from the latest upstream `master`, with the three Klio-specific patches from `leonardoce/kopia`s `klio-20260525` branch rebased on top:
- mTLS authentication
- `--tags` support
- gRPC stream interceptor for session-error logging
- Verified the rebased branch builds and passes `go vet` cleanly.

What's left

- Update Klio to build against `cloudnative-pg/kopia` (branch `klio`) instead of `leonardoce/kopia` (branch `klio-20260525`):
- `core/Dockerfile` (the `git clone` step that bulilds the `kopia` binary)
- `renovate.json`
- `AGENTS.md` (Key Dependencies section)
- a stale omment in `operator/test/e2e/otel_test.go`

The existing e2e suite will act as the regression check for this switch.

Start with the kopia clone step in core/Dockerfile, then inspect the corresponding references in renovate.json and the Key Dependencies section of AGENTS.md. Update the stale comment in operator/test/e2e/otel_test.go and run the existing end-to-end suite; done means Klio builds from cloudnative-pg/kopia's klio branch and the regression checks pass.

Written by the indexing model from the issue text.