[1.5.0] Ad existing vault: point user to recovery key

### Summary
After adding a vault (no matter if new or existing), users should be actively made aware of the recovery key

### Motivation
When creating a new vault, the user is actively made aware of the recovery key (and must confirm that he saved it). But if he just ads an existing vault, or if he migrates one, there's no popup. You have to remind on your own to look up the key in the vault options and save it.
As the recovery key might be relevant, there should be a note in every scenarios that adds a vault to cryptomator.