Alerting: Migrate unknown NoData\Error settings to the default (#68403)
* use default execution if legacy is not known
* update docs
* Update docs/sources/alerting/migrating-alerts/migrating-legacy-alerts.md
Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>
* Update docs/sources/alerting/migrating-alerts/migrating-legacy-alerts.md
Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>
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Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>
(cherry picked from commit 3af95bebe1)
Co-authored-by: Yuri Tseretyan <yuriy.tseretyan@grafana.com>