This change fixes a bug where lost/failed allocations are replaced by
allocations with the latest versions, even if the version hasn't been
promoted yet.

Now, when generating a plan for lost/failed allocations, the scheduler
first checks if the current deployment is in Canary stage, and if so, it
ensures that any lost/failed allocations is replaced one with the latest
promoted version instead.

To address review comments

`(alloc.DeploymentStatus == nil || !alloc.DeploymentStatus.IsCanary())`
and `!alloc.DeploymentStatus.IsCanary()` are equivalent.

Co-authored-by: Chris Baker <1675087+cgbaker@users.noreply.github.com>