http_proxy: use ngx.req.get_body_data to read the body

We cannot use resty.http's .get_client_body_reader().

The result of that is nil, and it results in a time-out in
some cases. Possibly because of this:
ledgetech/lua-resty-http#31

gateway/src/apicast/http_proxy.lua

@@ -85,12 +85,20 @@ local function current_path(uri)
 end
 
 local function forward_https_request(proxy_uri, uri)
+    -- This is needed to call ngx.req.get_body_data() below.
+    ngx.req.read_body()
+
     local request = {
         uri = uri,
         method = ngx.req.get_method(),
         headers = ngx.req.get_headers(0, true),
         path = current_path(uri),
-        body = http:get_client_body_reader(),
+
+        -- We cannot use resty.http's .get_client_body_reader().
+        -- The result of that is nil, and it results in a time-out in some
+        -- cases. Possibly because of this:
+        -- https://github.com/ledgetech/lua-resty-http/issues/31
+        body = ngx.req.get_body_data(),
     }
 
     local httpc, err = http_proxy.new(request)