By Trevor Hunnicutt, Josh Smith and Hyonhee Shin SEOUL (Reuters) – President Joe Biden and his new South Korean counterpart agreed on Saturday to hold bigger military drills and deploy more U.S. weapons if necessary to deter North Korea, while offering to send COVID-19 vaccines and potentially meet Kim Jong Un. Biden and Yoon Suk-yeol said their countries’ decades-old alliance needed to develop not only to face North Korean threats but to keep the Indo-Pacific region “free and open” and protect global supply chains. The two leaders are meeting in Seoul for their first diplomatic engagement sin…