### Describe Your Changes
With the recent release of Managed VictoriaMetrics users are able to
create and execute Alerting & Recording rules and send notifications via
hosted Alertmanager.
So, we're publishing Alertmanager configuration docs for Managed
VictoriaMetrics.
### Checklist
The following checks are **mandatory**:
- [x] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).
(cherry picked from commit 1106d91741)
