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/plugins.go

@@ -26,6 +26,7 @@ var (
 	Apps         map[string]*AppPlugin
 	Plugins      map[string]*PluginBase
 	PluginTypes  map[string]interface{}
+	Renderer     *RendererPlugin
 
 	GrafanaLatestVersion string
 	GrafanaHasUpdate     bool
@@ -58,6 +59,7 @@ func (pm *PluginManager) Init() error {
 		"panel":      PanelPlugin{},
 		"datasource": DataSourcePlugin{},
 		"app":        AppPlugin{},
+		"renderer":   RendererPlugin{},
 	}
 
 	pm.log.Info("Starting plugin search")