MINOR: ssl: support ssl-min-ver and ssl-max-ver with crt-list

SSL/TLS version can be changed per certificat if and only if openssl lib support
earlier callback on handshake and, of course, is implemented in haproxy. It's ok
for BoringSSL. For Openssl, version 1.1.1 have such callback and could support it.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 969734c..19c1132 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -10415,7 +10415,8 @@
         <crtfile> [\[<sslbindconf> ...\]] [[!]<snifilter> ...]
 
   sslbindconf support "npn", "alpn", "verify", "ca_file", "crl_file", "ecdhe",
-  "curves", "ciphers" configuration.
+  "curves", "ciphers" configuration. With BoringSSL "ssl-min-ver" and
+  "ssl-max-ver" are also supported.
   It override the configuration set in bind line for the certificate.
 
   Wildcards are supported in the SNI filter. Negative filter are also supported,