Add apps/x509 -set_issuer & -set_subject option to override issuer & subject

Add apps/x509 -set_issuer & -set_subject option to override issuer & subject

This changeset adds the counterpart to the '-subj' option to allow overriding
the Issuer. For consistency, the `-subj` option is aliased to `-set_subject`.

The issuer can be specified as following apps/openssl x509 -new -set_issuer
'/CN=example-nro-ta' -subj '/CN=2a7dd1d787d793e4c8af56e197d4eed92af6ba13' ...

This is useful in constructing specific test-cases or rechaining PKI trees

Joint work with George Michaelson (@geeohgeegeeoh)

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23257)