Document mongoc_ssl_opt_t and related "ssl" functions use TLS protocols. This ticket originally proposed deprecating mongoc_ssl_opt_t. Deprecating was rejected in PR#1796 due requiring application code changes with little expected benefit.

Original description:
SSL named URI options were deprecated in CDRIVER-2869.

Deprecate use of the mongoc_ssl_opts_t struct too. Users can pass most TLS options through the URI.

The options ca_dir and crl_file do not have URI options. Consider providing an opaque mongoc_tls_opts_t struct to provide these options.