Feature Request: Connection Pooling

[BusyByte]

Support pools of connections.

Maybe utilize lettus pool support somehow

Note: We did end up writing a pool using keypool. Not sure if we did it right but we're going to try it out and may end up contributing it back to redis4cats if it works out well for us.

[BusyByte]

@gvolpe one thing I had maybe noticed after we switched to our pooled solution with keypool is we get the blocking operations on the cpu warning when the pool is being filled on app startup. It don't think we saw these before switching to redis4cats and could be totally un-related and hard to track down exactly why these started. Does redis4cats block when the connection is made and need switched somehow to IO.blocking?

FYI: I'm still planning to contribute our pooling implementation back but haven't found the time yet.