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.

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

pkg/services/sqlstore/database_wrapper.go

@@ -119,6 +119,7 @@ func (h *databaseQueryWrapper) instrument(ctx context.Context, status string, qu
 
 	ctx = log.IncDBCallCounter(ctx)
 
+	// timestamp overridden and recorded AFTER query is run
 	_, span := h.tracer.Start(ctx, "database query", trace.WithTimestamp(begin))
 	defer span.End()