First, the title: The Eagles, in this context, are neither majestic birds nor Philadelphia football players, but the musical group that generated “Hotel California.” And Part 1 is not a hopeful tease for some possible future sequel. Part 1, the documentary that premieres tonight, covers the years from the group’s formation (and before, establishing the individual musical and psychological identities of members Don Henley, Glenn Frey, Joe Walsh and Timothy B. Schmit) to the grou