Allow testing backup in sylva 1.5

Arnaud Boutsrequested to merge
backport-1.5/backup into main

Add backup values file in release 1.5

The sylva-core MR succeeded: sylva-projects/sylva-core!5795 (merged)

tests are ok

-- Start backing up etcd from cluster 'mgmt-2086338277-kubeadm-capo'.
{"level":"info","ts":"2025-10-07T20:44:04.116388Z","caller":"snapshot/v3_snapshot.go:65","msg":"created temporary db file","path":"/tmp/tmp.gMCfDh/mgmt-2086338277-kubeadm-capo_etcd_backup_202510072044/mgmt-2086338277-kubeadm-capo_etcd_snapshot.db.part"}
{"level":"info","ts":"2025-10-07T20:44:04.122477Z","logger":"client","caller":"v3@v3.5.16/maintenance.go:212","msg":"opened snapshot stream; downloading"}
{"level":"info","ts":"2025-10-07T20:44:04.122509Z","caller":"snapshot/v3_snapshot.go:73","msg":"fetching snapshot","endpoint":"https://192.168.0.45:2379"}
{"level":"info","ts":"2025-10-07T20:44:05.259310Z","logger":"client","caller":"v3@v3.5.16/maintenance.go:220","msg":"completed snapshot read; closing"}
{"level":"info","ts":"2025-10-07T20:44:05.442817Z","caller":"snapshot/v3_snapshot.go:88","msg":"fetched snapshot","endpoint":"https://192.168.0.45:2379","size":"140 MB","took":"1 second ago"}
{"level":"info","ts":"2025-10-07T20:44:05.442907Z","caller":"snapshot/v3_snapshot.go:97","msg":"saved","path":"/tmp/tmp.gMCfDh/mgmt-2086338277-kubeadm-capo_etcd_backup_202510072044/mgmt-2086338277-kubeadm-capo_etcd_snapshot.db"}
Snapshot saved at /tmp/tmp.gMCfDh/mgmt-2086338277-kubeadm-capo_etcd_backup_202510072044/mgmt-2086338277-kubeadm-capo_etcd_snapshot.db
-- Etcd backed up.
-- Backup compressed.
Added `backup` successfully.
`/tmp/tmp.lhbPjB` -> `backup/backup/mgmt-2086338277-kubeadm-capo_etcd_backup_202510072044.tar.gz`
Total: 28.83 MiB, Transferred: 28.83 MiB, Speed: 58.38 MiB/s
-- Backup uploaded
Backup succeeded in 6 seconds
-- Push result to the pushgateway

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