Support SM2 certificate signing

SM2 certificate signing request can be created and signed by OpenSSL
now, both in library and apps.

Documentation and test cases are added.

Support SM2 certificate signing

SM2 certificate signing request can be created and signed by OpenSSL
now, both in library and apps.

Documentation and test cases are added.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9085)

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