Use regexes to match ALPN protocols (#5651)

nginx presents the client's list of ALPN protocols as
$ssl_preread_alpn_protocols, a comma-separated string.  Use regular
expressions to match each item in the list, rather than the exact value
of the entire list at once.

doc/debian/jitsi-meet/jitsi-meet.conf

     }
     # since 1.13.10
     map $ssl_preread_alpn_protocols $upstream {
-        "h2"            web;
-        "http/1.1"      web;
-        "h2,http/1.1"   web;
+        ~\bh2\b         web;
+        ~\bhttp/1\.     web;
         default         turn;
     }