By Shashank Nayar and Sruthi Shankar (Reuters) -Britain’s blue-chip index closed higher on Thursday, boosted by AstraZeneca’s gains following an upbeat sales forecast, while strong metal prices lifted mining stocks to their highest in more than a decade. The FTSE 100 index rose 0.4% and the gauge of industrial miners’ performance hit its highest since August 2011, buoyed by soaring prices of aluminium, copper and other base metals. [MET/L] AstraZeneca jumped 3.4% after the drugmaker raised its annual dividend for the first time in a decade and forecast higher sales for 2022, with new drugs aga…