Upstream: proxy_ssl_conf_command and friends.

Upstream: proxy_ssl_conf_command and friends.

Similarly to ssl_conf_command, proxy_ssl_conf_command (grpc_ssl_conf_command,
uwsgi_ssl_conf_command) can be used to set arbitrary OpenSSL configuration
parameters as long as nginx is compiled with OpenSSL 1.0.2 or later,
when connecting to upstream servers with SSL.  Full list of available
configuration commands can be found in the SSL_CONF_cmd manual page
(https://www.openssl.org/docs/man1.1.1/man3/SSL_CONF_cmd.html).