* app/vmbackupmanager: add metrics for better observability, include more information to `/api/v1/backups` API call response
* app/vmbackupmanager: drop old metrics before creating new ones
* app/vmbackupmanager: use `_total` postfix for counter metrics
* app/vmbackupmanager: remove `_total` postfix for gauge-like metrics
* app/vmbackupmanager: add `_last_run_failed` metrics for backups and retention
* app/vmbackupmanager: address review feedback
* app/vmbackupmanager: fix metric name
* app/vmbackupmanager: address review feedback, remove background updates of metrics, add restoring state of `_last_run_failed` metric from remote storage
* app/vmbackupmanager: improve performance for backup size calculation
* app/vmbackupmanager: refactor backup and retention runs to deduplicate each run logic
* {app/vmbackupmanager,lib/formatutil}: move HumanizeBytes into lib package
* app/vmbackupmanager: fix creating new metrics instead of reusing existing ones
* lit/formatutil: add comment to make linter happy
* app/vmbackupmanager: address review feedback
