Using the current_user data producer makes response uncacheable

When using the `current_user` data producer the response becomes uncacheable. This is because of this line:

https://github.com/drupal-graphql/graphql/blob/bf9dea39bedc0546df43018fddd398abf545b885/src/Plugin/GraphQL/DataProducer/User/CurrentUser.php#L73

As `$this->currentUser` is not an instance of `CacheableDependencyInterface`, the addCacheableDependency() method in `RefinableCacheableDependencyTrait` will fall back to setting the max age to 0:

https://git.drupalcode.org/project/drupal/-/blob/11.x/core/lib/Drupal/Core/Cache/RefinableCacheableDependencyTrait.php#L23

One option to fix this would be to not set any cacheability at all and leave this up to the consumers of the producer. But that would introduce quite a breaking change, as queries would suddenly become cacheable.

An alternative fix would be to implement a default behaviour that adds the `user` context (or sets the max age to 0), but introduces a new argument on the producer to prevent this from being done. That way existing implementation still work as before, while making it possible to customise the cacheability when needed.

Happy to do a merge request once the best approach has been found!