Fix embedded Alerting templates

User impact:

Currently some of our embedded alerting templates are broken and never fire an alert. For example: https://github.com/percona/pmm/blob/main/managed/data/iatemplates/mysql_down.yml

Problem affects this kind of queries:

sum by (service_name, node_name) (mysql_up) == 0

== 0  here works like a filter, so if mysql_up returns 1 this query in total will return nothing, but once mysql_up  return 0  whole query will return 0. And here is the problem, grafana triggers alert only on non-zero numeric data.

Solutions is dead simple, we need just to add bool after comparison operator.

sum by (service_name, node_name) (mysql_up) == bool 0

Steps to reproduce:

Actual result:

Expected result:

Workaround:

Details:

https://prometheus.io/docs/prometheus/latest/querying/operators/#comparison-binary-operators