Augment rand argument parsing to allow scaling

Augment rand argument parsing to allow scaling

Instead of just accepting a number of bytes, allows openssl rand to
accept a k|m|g suffix to scale to kbytes/mbytes/gbytes

Fixes #22622

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22624)