Billionaire Gautam Adani’s energy transmission unit is seeking to raise at least $500 million in foreign-currency debt by early next year, according to people familiar with the matter, as the company boosts infrastructure investments.   Adani Energy Solutions Ltd. is exploring multiple fundraising routes — including the so-called Regulation D bonds, a US framework which allows businesses to sell securities privately without going through the full public registration process.The total funds raised could go ...