DATAREDIS-308 - Add support for HyperLogLog.

We added methods for `PFADD`, `PFCOUNT` and `PFMERGE` to `RedisConnection` and `StringRedisConnection`.
`HyperLogLogOperations` available via `RedisTemplate` allow more indrect usage of HLL. 

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Please Note that currently Jedis is the only driver that can be used for HyperLogLog commands.