Miniscript: registration & signing

[benma]

There is a example CLI that works with this PR which:

• creates a miniscript policy
• registers it on the BB02
• generates a receive address
• signs a tx
• verifies that all steps are correct

https://github.com/digitalbitbox/bitbox02-api-go/pull/82

Run with go run cmd/miniscript/main.go.

The first commit here is the same as https://github.com/digitalbitbox/bitbox02-firmware/pull/1087