[token-cli] Fix panicking behavior from sign_only

[samkim-crypto]

Problem

In clap v2, the ArgMatches::is_present(ARG_NAME) function returns None when ARG_NAME is not defined in the clap app. In clap v3, ArgMatches::is_present(ARG_NAME) panics of ARG_NAME is not defined in the clap app.

I thought I fixed all occurrences of is_present that could panic in the token-cli, but it seems that I missed one place when we parse for Config.

`sign_only` is not an id of an argument or a group.
Make sure you're using the name of the argument itself and not the name of short or long flags.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Summary of Changes

Replace is_present with try_contains_id that does not panic.

[joncinque]

Makes sense, thanks!