* Renamed AccountLinkParams to SecretProvider and adapted descriptions to...

* Renamed AccountLinkParams to SecretProvider and adapted descriptions to "target account" instead of "account to link" which makes it a bit more generic
* Added generic method get_keypair_from_secret_provider that returns the keypair or an error
* Adapted `LinkAccount` & `ChangeOwnerKey` to use those
* Not sure the best place for the SecretProvider and new method - leaving in identity for now