[MRG + 1] Add fowlkess-mallows and other supervised cluster metrics to SCORERS...

[MRG + 1] Add fowlkess-mallows and other supervised cluster metrics to SCORERS dict so it can be used in hyper-param search (#8117)

* Add supervised cluster metrics to metrics.scorers

* Add all the supervised cluster metrics to the tests

* Add test for fowlkes_mallows_score in unsupervised grid search

* COSMIT: Clarify comment on CLUSTER_SCORERS

* Fix doctest