feat: support setting ICE ufrag and pwd

paullouisageneau/libjuice#243 allows setting
the ICE ufrag and pwd fields instead of generating random ones every
time.

paullouisageneau/libdatachannel#1201 exposes
config keys to allow setting the fields in libjuice from libdatachannel.

This PR allows setting the fields in libdatachannel from the PeerConnection
constructor.

It will require the two PRs above being merged an shipped before this
is ready for merging.

Refs: paullouisageneau/libdatachannel#1166

src/peer-connection-wrapper.cpp

@@ -234,6 +234,14 @@ PeerConnectionWrapper::PeerConnectionWrapper(const Napi::CallbackInfo &info) : N
         }
     }
 
+    // Override ICE ufrag/password if set
+    if (config.Get("iceUfrag").IsString()) {
+        rtcConfig.iceUfrag = config.Get("iceUfrag").As<Napi::String>().ToString();
+    }
+    if (config.Get("icePwd").IsString()) {
+        rtcConfig.icePwd = config.Get("icePwd").As<Napi::String>().ToString();
+    }
+
     // Create peer-connection
     try
     {