Add proxy support for get_from_cdn

discord/http.py

@@ -777,7 +777,15 @@ async def request(
             raise RuntimeError('Unreachable code in HTTP handling')
 
     async def get_from_cdn(self, url: str) -> bytes:
-        async with self.__session.get(url) as resp:
+        kwargs = {}
+
+        # Proxy support
+        if self.proxy is not None:
+            kwargs['proxy'] = self.proxy
+        if self.proxy_auth is not None:
+            kwargs['proxy_auth'] = self.proxy_auth
+
+        async with self.__session.get(url, **kwargs) as resp:
             if resp.status == 200:
                 return await resp.read()
             elif resp.status == 404: