This is useful to force on-interactive mode with automatic key selection. In unit tests this is necessary. When debugging a test on a real terminal interactive mode is not desired
When creating a new clan, the key selection now looks like this:
```
Found existing admin keys on this machine:
1: type: AGE
pubkey: age1xyz...
source: /home/grmpf/.config/sops/age/keys.txt
2: type: PGP
pubkey: abc...
source: SOPS_PGP_FP
Select keys to use (comma-separated list of numbers, or leave empty to select all):
```
This is achieved by adding a `source` attribute to `SopsKey`.
- generate keys in ./sops instead of ./sops/vars for now
- don't initialize all flakes with sops keys, only generate when needed
- use the new 'clan vars keygen' in tests
