[Bugfix] : Disable conditional request feature outside API and does not overwrite existing ETag

Ensure the conditional request feature (setting an ETag and returning a 304) is not applied to routes outside API.
Also ensures this feature does not overwrite a custom ETag already set by the user.

Fix #141
This is going to have to be changed up here because it will only work for responses that are instances of `Illuminate\Http\Response`. You'll probably have to shift the `$this->requestTargettingApi($request)` into its own statement and have the `instanceof` in another.