Integrate migration monitor to the flow for better tracking of migration dry runs

[seadanda]

The backend can be run locally, instructions here: https://github.com/paritytech/asset-hub-migration-monitor

Then you can specify the port in the hosted migration monitor at https://migration.paritytech.io

When paritytech/asset-hub-migration-monitor#10 is implemented, this could be done more easily by automatically opening a browser at https://migration.paritytech.io?backend_url=http://localhost:3000