vmalert: support `limit` param in groups definition
`limit` param limits number of time series samples produced by a single rule
during execution.
On reaching the limit rule will return an err.
Signed-off-by: lihaowei <haoweili35@gmail.com>
* vmalert: support rules backfilling (aka `replay`)
vmalert can `replay` configured rules in the past
and backfill results via remote write protocol.
It supports MetricsQL/PromQL storage as data source,
and can backfill data to remote write compatible
storage.
Supports recording and alerting rules `replay`. See more
details in README.
https://github.com/VictoriaMetrics/VictoriaMetrics/issues/836
* vmalert: review fixes
* vmalert: readme fixes
