Backend image rendering as plugin (#11966)

* rendering: headless chrome progress

* renderer: minor change

* grpc: version hell

* updated grpc libs

* wip: minor progess

* rendering: new image rendering plugin is starting to work

* feat: now phantomjs works as well and updated alerting to use new rendering service

* refactor: renamed renderer package and service to rendering to make renderer name less confusing (rendering is internal service that handles the renderer plugin now)

* rendering: now render key is passed and render auth is working in plugin mode

* removed unneeded lines from gitignore

* rendering: now plugin mode supports waiting for all panels to complete rendering

* fix: LastSeenAt fix for render calls, was not set which causes a lot of updates to Last Seen at during rendering, this should fix sqlite db locked issues in seen in previous releases

* change: changed render tz url parameter to use proper timezone name as chrome does not handle UTC offset TZ values

* fix: another update to tz param generation

* renderer: added http mode to renderer service, new ini setting [rendering] server_url

vendor/github.com/prometheus/common/expfmt/decode.go

@@ -164,9 +164,9 @@ func (sd *SampleDecoder) Decode(s *model.Vector) error {
 }
 
 // ExtractSamples builds a slice of samples from the provided metric
-// families. If an error occurs during sample extraction, it continues to
+// families. If an error occurrs during sample extraction, it continues to
 // extract from the remaining metric families. The returned error is the last
-// error that has occured.
+// error that has occurred.
 func ExtractSamples(o *DecodeOptions, fams ...*dto.MetricFamily) (model.Vector, error) {
 	var (
 		all     model.Vector