Previews: refactor (#47728)

* #44449: return standard thumb service even if auth setup fails

* #44449: remove dashboardPreviewsScheduler feature flag

* #44449: externalize dashboardPreviews config

* #44449: disable previews by default

* #44449: rename logger

* #44449: dashboardPreviewsAdmin feature requires dev mode

* #44449: retrigger CII

pkg/setting/setting.go

@@ -439,6 +439,8 @@ type Cfg struct {
 
 	// Query history
 	QueryHistoryEnabled bool
+
+	DashboardPreviews DashboardPreviewsSettings
 }
 
 type CommandLineArgs struct {
@@ -1001,6 +1003,8 @@ func (cfg *Cfg) Load(args CommandLineArgs) error {
 
 	cfg.readDataSourcesSettings()
 
+	cfg.DashboardPreviews = readDashboardPreviewsSettings(iniFile)
+
 	if VerifyEmailEnabled && !cfg.Smtp.Enabled {
 		cfg.Logger.Warn("require_email_validation is enabled but smtp is disabled")
 	}