How to test:

1. Go to the alert rule templates tab and check if `Backup Failed` template exists

2. Create alert rule from that template

3. Go to the backups pages

4. Create valid S3 storage location

5. Create successful on demand backup

6. Wait couple of minutes and check that there is no fired alets

7. Break you storage location (for example remove one letter from access key) and save it

8. Create another on demand backup that should fail in that case

9. In one minute you should see related alert on fired alerts tab

How to document:

With this ticket we introduce two changes:

1. New metric `pmm_managed_backups_artifacts` that reflects state of backup artifacts

2. New alert rule template that notifies user about backup errors

Demo:

https://drive.google.com/file/d/1JaEbC7ug0OUfKt6MP8q_JYgHH5nM6411/view?usp=drive_link