supports setting json opt per request

lib/transport/node-fetch.js

@@ -56,6 +56,12 @@ class FetchTransport extends Transport {
     return opts;
   }
 
+  parseAsJson(ctx, contentType) {
+    if (ctx.opts?.json !== undefined) return ctx.opts.json;
+
+    return this.defaults?.json || contentType?.includes('json');
+  }
+
   async toResponse(ctx, from) {
     const to = ctx.res;
     REQUIRED_PROPERTIES.forEach((property) => {
@@ -67,9 +73,8 @@ class FetchTransport extends Transport {
 
     // currently supports json and text formats only
     to.body = await from.text();
-
     const contentType = to.headers['content-type'];
-    if (this.defaults?.json || contentType?.includes('json')) {
+    if (this.parseAsJson(ctx, contentType)) {
       try {
         to.body = JSON.parse(to.body);
       } catch {} // If body is not parseable, leave as text