chore: Remove template Callbacks

[BagritsevichStepan]

No description provided.

[romange]

@BagritsevichStepan please see #4368
I do not understand why callback is needed at all

[BagritsevichStepan]

@BagritsevichStepan please see #4368 I do not understand why callback is needed at all

It was used just to reduce boilerplate code. And we are now performing the same check twice:

if (!parsed_json) {
    VLOG(1) << "got invalid JSON string '" << json_str << "' cannot be saved";
    return OpStatus::INVALID_VALUE;
  }

[romange]

I think this is not justified to change interfaces of function to save a few lines. Moreover, it actually had a bug of copying a json object instead of moving it. With memory allocators is becomes a correctness bug where we probably loose the correct resource. All this is not worth it.