No matter how talented a person is, it always helps to have friends in high places to help spread the word about those abilities. Guitarist Sanjay Mishra, who will be leading a group on Wednesday at Blues Alley, must understand this as well as anyone. His big break came in 1995 with the release of Blue Incantation, an album whose chief supporter was none other than the late Jerry Garcia. The Grateful Dead stalwart not only released the recording through the Dead’s merchandising company, but also performed on three of its tracks, making it one of his final recordings.