Document that the certificate passed to SSL_CTX_add_extra_chain_cert()
should not be freed by the application.
PR#3409
(cherry picked from commit 0535c2d67ca2d684087ef90be35d5fb207aab227)
Add restrictions section present in other branches.
Conflicts:
doc/ssl/SSL_CTX_add_extra_chain_cert.pod
(cherry picked from commit 86cac6d3b25342ff17a2b6564f7592fd7c6829e8)