Fix arg group syntax

[MarcusGrass]

The clap arg-group needs the field name of the struct

Otherwise you get this:

thread 'main' panicked at 'Command list-messages: Argument group 'list-messages' contains non-existent argument 'recipient-uuid'', /home/user/.cargo/registry/src/index.crates.io-6f17d22bba15001f/clap_builder-4.3.19/src/builder/debug_asserts.rs:292:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

After:

error: the following required arguments were not provided:
  <--recipient-uuid <RECIPIENT_UUID>|--group-master-key <GROUP_MASTER_KEY>>

Usage: presage-cli list-messages <--recipient-uuid <RECIPIENT_UUID>|--group-master-key <GROUP_MASTER_KEY>>

For more information, try '--help'.

Which is expected

[gferon]

Thanks!