please implement `gosop generate-key --signing-only`

[dkg]

sop generate-key should have an option --signing-only:

The presence of the --signing-only option is intended to create a key that is only capable of signing, not decrypting. This is useful for deployments where only signing and verification are necessary.

0  dkg@bob:~$ gosop generate-key --signing-only test key
Incorrect Usage: flag provided but not defined: -signing-only

NAME:
   gosop generate-key - Generate a Secret Key

USAGE:
   gosop generate-key [command options] [USERID...]

COMMANDS:
   help, h  Shows a list of commands or help for one command

OPTIONS:
   --no-armor                 (default: false)
   --profile value            --profile=PROFILE (default: "default")
   --with-key-password value  --with-key-password=PASSWORD
   --help, -h                 show help
2025/02/20 22:31:29 flag provided but not defined: -signing-only
1 dkg@bob:~$ gosop version --extended
gosop 1.1.0
GopenPGP 3.1.0
Compiled using go1.23.5
0 dkg@bob:~$ 

[dkg]

Just adding a gentle nudge on this request. The setup-sopv-test script uses sop generate-key --signing-only, which means that i can't currently use gosop to generate a test suite to evaluate other sopv implementations.