APPS: Improve diagnostics on missing/extra args and unknown cipher/digest

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16450)

find-doc-nits: Make -c option (cmd-nits) independent of app build and execution

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15298)