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`.
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