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

pkg/plugins/backend_utils.go

@@ -0,0 +1,19 @@
+package plugins
+
+import (
+	"fmt"
+	"runtime"
+	"strings"
+)
+
+func ComposePluginStartCommmand(executable string) string {
+	os := strings.ToLower(runtime.GOOS)
+	arch := runtime.GOARCH
+	extension := ""
+
+	if os == "windows" {
+		extension = ".exe"
+	}
+
+	return fmt.Sprintf("%s_%s_%s%s", executable, os, strings.ToLower(arch), extension)
+}