Add bind-time capability to inject kind migrations as Go funcs

[sdboyer]

With grafana/thema#187 merged, we can now add a layer here that wraps that capability for having Go migration funcs, but doesn't expose *thema.Instance in the required func signature. My guess is that the best means for doing it for Core/Custom kinds will be to use our unstructured object type. We can probably skip support for Composable kinds for an initial pass.

As with the thema implementation, i expect we implement this as an option that can be passed to BindCore or BindCustom - a slice of funcs that do the migrations. The thema-based implementation will just pass those down to BindLineage after wrapping them in a dynamic func that just converts to and from the *thema.Instance type.