Installs Squid Mesh by creating its migration in the host application.
Usage
$ mix squid_mesh.install
This task creates one current-schema Squid Mesh 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. Squid Mesh assumes
the host application owns the delivery backend and worker loop used to call
SquidMesh.execute_next/1.