Installs Squidie by creating its migration in the host application.
Usage
$ mix squidie.install
This task creates one current-schema Squidie migration in
priv/repo/migrations so the host application can run it through its normal
Ecto migration flow.
Backend-specific migrations are intentionally not copied. Squidie assumes
the host application owns the delivery backend and worker loop used to call
Squidie.execute_next/1.