Execute right away for Safes with threshold 1

[jfschwarz]

If a Safe uses a threshold of 1 and I'm executing as an owner of the Safe, atm the transaction will only be signed and proposed via the transaction service. It should actually be directly executed in that case, though.

ser-kit actually already covers this logic but relies on the Safe waypoint's threshold field for that. We don't provide this field in our manually created routes.

We should get rid of the legacy connection migration functions and directly operate on the new routes model. This allows us to populate the threshold field once the user enters a Safe address and we fetch the Safe info.