feat: Support for setting aggregation for (Hybrid)RouteLayer (#202)

* Enable to set top_k for RouteLayer

* Add top_k unit test for RouteLayer

* Added support for setting different aggregation method for HybridRL

* Add unit test to verify that aggregation works

* Add support for setting aggregation in RouteLayer

* Fix bug where agg method not used in RL

* Add tests for agg

* Linted code

* Updated codecov file

* Change aggregation method names to lower case

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Co-authored-by: James Briggs <35938317+jamescalam@users.noreply.github.com>