[Feature Request] Selection filter for random speaker/conversation/utterance corpus functions

[vianxnguyen]

It would be nice for corpus functions such as random_speaker(), random_conversation(), etc to have a selection filter, for example, to get a random speaker that satisfies a condition. This could be useful in data exploration, in cases where the user wants to get a speaker with a certain role, or a conversation with at least a certain length, etc.