Rivers belong where they can ramble,/ Eagles belong where they can fly,/ I’ve got to be where the eagles run free,/ Gotta find my corner of the sky• So goes the lyric of one of the many songs which six-time Tony Award-nominated (including “Wicked” and “Godspell”) composer Stephen Schwartz wrote for “Pippin, the Musical.” This show, with book by Roger O. Hirson, premiered on Broadway in 1972 and is about the son of King Charles (Charlemagne) and his many adventures while …