Allow white labeling loading logo (#36174)

* Allow to whitelabeling loading logo

* Add loading_logo to documentation

* Change loading_logo to loading_logo_url

docs/sources/enterprise/white-labeling.md

@@ -25,6 +25,7 @@ You can change the following elements:
 - Login title (will not appear if a login logo is set, Grafana v7.0+)
 - Login subtitle (will not appear if a login logo is set, Grafana v7.0+)
 - Login box background (Grafana v7.0+)
+- Loading logo
 
 > You will have to host your logo and other images used by the white labeling feature separately. Make sure Grafana can access the URL where the assets are stored.
 
@@ -62,6 +63,9 @@ The configuration file in Grafana Enterprise contains the following options. Eac
 
 # Set to complete URL to override apple/ios icon
 ;apple_touch_icon =
+
+# Set to complete URL to override loading logo
+;loading_logo_url =
 ```
 You can replace the default footer links (Documentation, Support, Community) and even add your own custom links.
 An example follows for replacing the default footer and help links with new custom links.

pkg/api/dtos/index.go

@@ -26,6 +26,7 @@ type IndexViewData struct {
 	AppTitle                string
 	Sentry                  *setting.Sentry
 	ContentDeliveryURL      string
+	LoadingLogo             template.URL
 	// Nonce is a cryptographic identifier for use with Content Security Policy.
 	Nonce string
 }

pkg/api/index.go

@@ -470,6 +470,7 @@ func (hs *HTTPServer) setIndexViewData(c *models.ReqContext) (*dtos.IndexViewDat
 		Sentry:                  &hs.Cfg.Sentry,
 		Nonce:                   c.RequestNonce,
 		ContentDeliveryURL:      hs.Cfg.GetContentDeliveryURL(hs.License.ContentDeliveryPrefix()),
+		LoadingLogo:             "public/img/grafana_icon.svg",
 	}
 
 	if hs.Cfg.FeatureToggles["accesscontrol"] {