* vmalert: allow extra GET params in datasource package
ExtraParams will be added as GET params to every HTTP request made by datasource.
The `roundDigits` param, for example, was substituted by corresponding extra param.
* vmalert: add nocache=1 param for replay process
The `nocache=1` param is VictoriaMetrics specific parameter which prevents it
from caching and boundaries aligning for queries. We set it to avoid cache
pollution in `replay` mode and also to avoid unnecessary time range boundaries
alignment.
* vmalert: mention nocache=1 in replay description
* vmalert: fix bug with unused param
* vmalert: fix mistake with object reuse while parsing response
During the refactoring, the wrong optimisations was applied in
parse function which caused metric fields reset. The change removes
optimisation.
https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1369
* vmalert: add test to cover multiple metrics in one response
* 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
