Add support for countDocuments

[mhdzumair]

Hi, i see that the model doesn't have function for countDocuments as in the mongo. According to mongo doc, https://www.mongodb.com/docs/manual/reference/method/db.collection.count/#inaccurate-counts-without-query-predicate

I haven't seen any inaccurate results, however I felt like a bit of difference in response time when using the below code. I'm not 100% about the benchmark due to using external DB through internet.

count = await TorrentStreams.count()

collection = TorrentStreams.get_motor_collection()
count = await collection.count_documents({})