Make SRP_CTX.info ownership and lifetime be the same as SRP_CTX.login.

Ownership and lifetime rules of SRP_CTX.info are confusing and different
from those of SRP_CTX.login, making it difficult to use correctly.
This makes the ownership and lifetime be the same as those of SRP_CTX.login,
thet is a copy is made when setting it and is freed when SRP_CTX is freed.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3467)