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/beorn7/perks/quantile/stream.go

@@ -77,15 +77,20 @@ func NewHighBiased(epsilon float64) *Stream {
 // is guaranteed to be within (Quantile±Epsilon).
 //
 // See http://www.cs.rutgers.edu/~muthu/bquant.pdf for time, space, and error properties.
-func NewTargeted(targets map[float64]float64) *Stream {
+func NewTargeted(targetMap map[float64]float64) *Stream {
+	// Convert map to slice to avoid slow iterations on a map.
+	// ƒ is called on the hot path, so converting the map to a slice
+	// beforehand results in significant CPU savings.
+	targets := targetMapToSlice(targetMap)
+
 	ƒ := func(s *stream, r float64) float64 {
 		var m = math.MaxFloat64
 		var f float64
-		for quantile, epsilon := range targets {
-			if quantile*s.n <= r {
-				f = (2 * epsilon * r) / quantile
+		for _, t := range targets {
+			if t.quantile*s.n <= r {
+				f = (2 * t.epsilon * r) / t.quantile
 			} else {
-				f = (2 * epsilon * (s.n - r)) / (1 - quantile)
+				f = (2 * t.epsilon * (s.n - r)) / (1 - t.quantile)
 			}
 			if f < m {
 				m = f
@@ -96,6 +101,25 @@ func NewTargeted(targets map[float64]float64) *Stream {
 	return newStream(ƒ)
 }
 
+type target struct {
+	quantile float64
+	epsilon  float64
+}
+
+func targetMapToSlice(targetMap map[float64]float64) []target {
+	targets := make([]target, 0, len(targetMap))
+
+	for quantile, epsilon := range targetMap {
+		t := target{
+			quantile: quantile,
+			epsilon:  epsilon,
+		}
+		targets = append(targets, t)
+	}
+
+	return targets
+}
+
 // Stream computes quantiles for a stream of float64s. It is not thread-safe by
 // design. Take care when using across multiple goroutines.
 type Stream struct {