Redis store

[claudiuchis]

Hi Alexey,

I created a version of the Redis event store that is using a Redis function to add events to streams and to the _all stream in a single transaction. As per Redis documentation (https://redis.io/docs/manual/programmability/functions-intro/#what-are-redis-functions):

"Like all other operations in Redis, the execution of a function is atomic. A function's execution blocks all server activities during its entire time, similarly to the semantics of transactions."

I've created just the event store and corresponding tests, but if you think this is worth adding to the main repo, then I can add the additional parts, e.g. subscriptions and producers.

[CLAassistant]

All committers have signed the CLA.

[alexeyzimarev]

Would be nice to have a test that appends and then reads the event. Seems like reads aren't covered in tests. For some reason I had an impression that your fork had tests for reads?