[Http][Response] Add the remember function

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #3030

This feature adds the `remember` function to `JsonResponse.php` and `Response.php`. This function allows to:
- set ETag and/or Last-Modified response header.
- check against the `Request` instance if the `Response` has been modified.
- If so, set the `Response` as not modified (304)