chore(tracing): add tracing for frontend and db session (#91509)

This PR adds instrumentation for loading frontend SPA along with select methods in the dashboard service, and cleans up span handling in sqlstore.

---------

Co-authored-by: Dave Henderson <dave.henderson@grafana.com>

pkg/api/dashboard.go

@@ -82,7 +82,7 @@ func dashboardGuardianResponse(err error) response.Response {
 // 404: notFoundError
 // 500: internalServerError
 func (hs *HTTPServer) GetDashboard(c *contextmodel.ReqContext) response.Response {
-	ctx, span := hs.tracer.Start(c.Req.Context(), "httpserver.GetDashboard")
+	ctx, span := hs.tracer.Start(c.Req.Context(), "api.GetDashboard")
 	defer span.End()
 
 	uid := web.Params(c.Req)[":uid"]
@@ -262,6 +262,9 @@ func (hs *HTTPServer) getUserLogin(ctx context.Context, userID int64) string {
 }
 
 func (hs *HTTPServer) getDashboardHelper(ctx context.Context, orgID int64, id int64, uid string) (*dashboards.Dashboard, response.Response) {
+	ctx, span := hs.tracer.Start(ctx, "api.getDashboardHelper")
+	defer span.End()
+
 	var query dashboards.GetDashboardQuery
 
 	if len(uid) > 0 {