ANN ARBOR, Mich. — Behind Spike Lee and a documentary film crew, amid the curious bystanders and the assortment of unemployed pass-catchers, there was a quarterback and a coach. And Saturday afternoon, in the middle of Michigan’s annual spring football renewal, that was where everyone’s attention turned, if only for 15 minutes or so. Not just because the coach allowed it, either. He encouraged it. Championed it, even. Colin Kaepernick was in the Big House, and whether you think that’s a big deal or not — and whatever the reasons for feeling that way, politically or otherwise — that was the poi…