storcon: Attached(0) tenants that do graceful migrations can get stuck

[jcsp]

This is not an issue in the field where we always used Attached(1) (i.e. 1 secondary location).

If we use Attached(0), and the scheduling optimisation logic tries to move a location by creating a secondary and waiting for it to warm up, then this can get stuck because the attached location never uploads a heatmap for the secondary to use.

The attached location only uses the PlacementPolicy to decide whether to enable heatmaps. We should either do it always, or respect the number of secondaries in the intent as well as the placement policy.